1 - Calibration with Nanosec

You can include the Finetune and Nanosec faces in your Sensor Watch firmware to achieve exceptionally high accuracy within 10 seconds per year.

Accurate timekeeping with a quartz crystal

The Sensor Watch measures time using a quartz crystal that oscillates at a frequency of 32,768 kHz. In practice, the frequency of every crystal deviates a little from the nominal value. Because the difference is very small, we don’t express it as a percentage (“parts per hundred”), but as ppm (“parts per million”). For example, a deviation of +1 ppm means the frequency is 32,768.03278 kHz. This would make the watch gain about 31.5 seconds per year, because there are about 31.5 million seconds in a year.

In addition to the static offset of individual crystals, their frequency also varies dynamically with temperature. Crystals are manufactured in a way that their frequency peaks at 25 °C and decreases at both higher and lower temperatures.

For accurate timekeeping, you need to correct for your crystal’s static frequency offset, and your watch needs to dynamically compensate for the variation due to temperature changes. These are the things that the Nanosec and Finetune watch faces let you do.

Calibrating the Sensor Watch

For really good results you need a watch with a temperature sensor, but you can also get a significant improvement without one. Without a temperature sensor, select correction profile P1 instead of the default P3 (details in the last section).

The firmware has to include these faces:

  • A regular clock face like Simple Clock (simple_clock_face), because you want a way to see the time;
  • Time Set (set_time_face), because you need a way to set the date and time;
  • Finetune (finetune_face), so you can set the time precisely and adjust the static frequency correction;
  • Nanosec (nanosec_face), because it contains the behind-the-scenes magic that dynamically compensates for temperature-driven variation.

To calibrate your watch, follow these steps:

  1. Flash a firmware that contains the necessary faces onto the watch, assemble it, and set the time via the Time Set face.

  2. Open time.is in a browser to display the accurate time. Go to the Finetune face and adjust the offset until the seconds on the watch precisely match the seconds on the screen. Apply the change without updating the frequency correction value with a long ALARM press.

    See the Finetune section below for the details of doing this.

  3. Wait a few days, then fine-tune your watch again using time.is and Finetune, saving your changes with a long LIGHT press. Your watch now knows how many hours have passed since the last time it was accurate, and how much it has drifted since then. From these two values Finetune can calculate an update to the static frequency correction value, beyond adjusting the current time itself.

  4. Your watch is now a lot more accurate. Wait a few weeks until it has drifted a second or two, then repeat Step 3.

  5. Wait a few months, then repeat Step 3. At this stage your Sensor Watch will be accurate to within 10 seconds per year.

Some useful details:

  • You need a special site like time.is for this type of calibration. The normal time on most websites (and on most devices like laptops or smartphones) is not accurate enough.
  • The Finetune face lets you adjust the time in increments of 25 msec. That is below most people’s threshold of perception. You need to wait for the watch to build up a noticeable amount of drift before re-calibration is practical.
  • The static frequency correction value is preserved when the watch resets. You don’t need to calibrate from scratch after replacing the battery or re-flashing the firmware.
  • The 10 seconds per year accuracy puts your watch right up there with the most expensive high-end quartz timekeepers.


When you reach Finetune by repeatedly pressing MODE to cycle through the installed watch faces, it will first look a little like this:

The four 0s mean that you haven’t input any time adjustment yet. The number on the right keeps updating to show the seconds part of the current time.

Finetune has two secondary faces. You need a long MODE press to move to the first of them; after that, a short press is enough.

  • FT means Finetune, and it’s the main screen where you can enter the desired time adjustment.
  • DT stands for delta time and it shows the number of hours since you last adjusted the time with the Finetune face. At first you will see a small value like this because your watch hasn’t been on for very long yet. The small numbers are fractional hours. E.g., the image above shows 0.05 hours, which is 3 minutes.
  • F stands for frequency, and it shows the amount by which your current adjustment will update the static frequency correction value. However, unless at least 6 hours have passed, Finetune will not mess with the frequency correction, which is why at first you will see “6Hr” here.
  • Back on the main screen, you can use LIGHT and ALARM to change the adjustment. A long LIGHT press increases the offset by 250 msec; a short LIGHT press adds 25 msec.
  • The first and third digits of the display have some limitations, which is why the “7” in 0275 looks a bit odd.
  • You need to go towards a positive value as shown above if your watch is ahead of the true time.
  • You can verify the adjustment’s effect by holding your watch next to the time on an accurate clock, like time.is. Your adjustment offsets the constantly ticking seconds value.
  • A long ALARM press decreases the value by 250 msec. A short ALARM press decreases it by 25 msec.
  • The odd shape in the top right is meant to be a double minus sign, indicating that this is a negative adjustment.
  • You need a negative adjustment if your watch is behind the true time.

Now let’s see what a real calibration looks like!

  • On the FT screen I have input an offset of 1025. My watch was just a bit over a second fast.
  • The DT screen tells me that 693.72 hours, or a little over four weeks, have passed since the last time I adjusted the time with Finetune.
  • The F screen tells me that if I apply this adjustment, the static time correction value will increase by 0.4104 ppm. (This will make my watch about 12.9 seconds slower per year.)
  • A long LIGHT press applies the adjustment to the time and updates the static time correction value. This is what I did above. Sensor Watch will be more accurate going forward!
  • A long ALARM press applies the adjustment to the time but does not update the static frequency correction. This is what you need to do the very first time you use Finetune, when you initially set the exact time.
  • After either a long LIGHT or long ALARM press on the F screen, Sensor Watch returns to the default face that shows the current time.

What if you have come to the Finetune face only to experiment but do not want to change the time, let alone mess with Sensor Watch’s calibration? Easy: on the FT screen, change the value 0000 again. If you now press MODE a couple of times, Sensor Watch will move on from Finetune. Or if you just wait for a minute without pressing anything, it will return to the Simple Time screen.


The Nanosec face has two functions. The first of the two is invisible but absolutely crucial. The face contains code that Sensor Watch executes regularly in the background. This code dynamically adjusts the time in minuscule increments to compensate for the effects of the current temperature on the crystal’s frequency.

The second, visible function is a collection of screens where you can review and change various parameters that affect Nanosec’s internal calculations. You essentially won’t need to change any of these settings, but they are fun to review.

In each of the screens below, you can use LIGHT to increase the value and ALARM to decrease it. Where it makes sense, a long press means a larger change.

  • FC: The static frequency correction value.
  • T0: The crystal’s center temperature, in °C. Nominally this is 25 °C for all crystals, but small variations are possible. A true center temperature improves the precision of dynamic frequency adjustments. However, in order to determine this value, a number of fine measurements are needed at controlled temperatures, which is beyond the reach of most Sensor Watch users.
  • 2C: The quadratic coefficient in the formula that Nanosec uses to approximate the quartz crystal’s temperature characteristics.
  • 3C: The cubic coefficient in the formula that Nanosec uses to approximate the quartz crystal’s temperature characteristics.
  • PR: The correction profile (formula) used to model the crystal’s temperature characteristics. You will most likely want to stick with P3, but see description of profiles below.
  • CD: The cadence of time correction, i.e., the length of the interval (in minutes) at which Nanosec makes a minuscule adjustment to the time.
  • AA: Aging compensation (ppm/year). The static frequency of crystals changes with age, but the exact value can only be determined empirically. If you notice that you keep adding 0.5 ppm each year to the static frequency correction to stay accurate, you can instead enter that value here.

Nanosec correction profiles

This is what the various correction profiles do.

P0: Static hardware correction with 1ppm resolution. This has the least additional power draw because the correction is done entirely in the hardware.

P1: High-resolution (0.01ppm) static correction implemented in software. This is the profile you’d want to choose if your watch has no temperature sensor.

P2: High-resolution static correction, plus dynamic frequency correction for temperature changes. The dynamic correction uses the quadratic formula from the crystal’s datasheet.

P3: Like P2, both static and dynamic correction, but using an empirically measured cubic formula.

P4: Custom settings for a specific crystal, using values that you can edit in the source code. You need to determine these values yourself; your crystal is unlikely to match what you find in the source code.

2 - Clocks

The core function of a watch is telling time. All of the watch faces in this category tell time in one form or another.

Beat Time


The Beat Time face displays the current Swatch Internet Time, or .beat time. This is a decimal time system that divides the day into 1000 beats.

The three large digits in the bottom row indicate the current beat, and the two smaller digits (normally the seconds in Simple Clock) indicate the fractional beat; so for example you can read “67214” as “beat 672.14”.

Binary LED Clock


A “fork” of the simple clock face, which provides the functionality of showing the current time by flashing the LED using binary representation.

This feature serves as a practical solution to compensate for the admittedly subpar backlight of the F91w watch and is especially useful if your eyesight is not the best. By pressing and holding the light button long enough, the watch will illuminate the LED to showcase the current time.

How to interpret the flashing led:

  • Firstly, the hour is presented as a binary number, with the lowest bit displayed first. A short flash signifies 0, while a longer flash represents 1. If you use the watch in 24h mode, please note that the indicated value may be decreased by 12, to keep things simple and short. For example, 22h would be translated to 10h.
  • After showing the hour, a lengthier pause indicates that minutes will be shown next.
  • Similar to the hour representation, minutes are displayed in binary format, starting with the lowest bits. A short flash denotes 0, a longer flash represents 1.

Decimal Time


This face presents the current time as hours and hundredths of an hour. Every hundreth of an hour, or “centihour”, occurs every 36 seconds. Because they range from 0 to 99, centihours, in the seventies range, will be displayed with a lowercase 7.

This method of timekeeping is used by the United States Postal Service.

This method may be used by other organizations as well

Many thanks go to Joey Castillo for making this project happen.

Mars Time


This watch face is dedicated to Martian timekeeping. It has several modes, and can display either a time or a date. Pressing the Alarm button cycles through different time zones on Mars:

  • MC - Mars Coordinated Time, the time at Airy-0 Crater on the Martian prime meridian
  • ZH - Local mean solar time for the Zhurong rover
  • PE - LMST for the Perseverance rover
  • IN - LMST for the Insight lander
  • CU - LMST for the Curiosity rover

Press the Light button to toggle between displaying time and date:

  • MC S - the Mars Sol Date, Martian days since December 29, 1873
  • ZH Sol - Mission sol for the Zhurong rover
  • PE Sol - Mission sol for the Perseverance rover
  • IN S - Mission sol for the InSight lander
  • CU S - Mission sol for the Curiosity rover

Note that where the mission sol is below 1000, this watch face displays the word “Sol” on the bottom line. When the mission sol is over 1000, the word “Sol” will not fit and so it displays a stylized letter S at the top right.

Repetition Minute


A hopefully useful complication for friendly neighbors in the dark

Originating from 1676 from reverend and mechanician Edward Barlow, and perfected in 1820 by neighbor Abraham Breguet, a minute repeater or “repetition minute” is a complication in a mechanical watch or clock that chimes the hours and often minutes at the press of a button. There are many types of repeater, from the simple repeater which merely strikes the number of hours, to the minute repeater which chimes the time down to the minute, using separate tones for hours, quarter hours, and minutes. They originated before widespread artificial illumination, to allow the time to be determined in the dark, and were also used by the visually impaired.

How to use it :

  • Long press the light button to get an auditive reading of the time like so :
  • 0..23 (1..12 if 24-hours format isn’t enabled) low beep(s) for the hours
  • 0..3 low-high couple pitched beeps for the quarters
  • 0..14 high pitched beep(s) for the remaining minutes

Prerequisite : a watch with a working buzzer

~ Only in the darkness can you see the stars. - Martin Luther King ~

Simple Clock


The Simple Clock watch face echoes the classic time and date display of the stock F-91W. It displays the day of the week and day of the month on the top line, along with the current time on the bottom line. Pressing the Light button illuminates the LED so that you can read the display in the dark. Holding the Light button keeps the LED on while the button is held.

If you soldered the buzzer connector to your Sensor Watch board, you may also toggle the Hourly Chime feature by pressing and holding the Alarm button. When you release the Alarm button, the Signal indicator will turn on, indicating that the hourly chime is enabled.

The Simple Clock face also incorporates a low battery warning: this watch face will display the LAP indicator when it detects that the battery voltage is low. This does not mean that power failure is imminent, but it does mean that your battery has only about 5% of its original capacity remaining and you should start thinking about a replacement. The battery is a CR2016 coin cell.

Week Number Clock


Same as simple clock, but has iso 8601 week number instead of seconds counter.

Long-press ALARM to toggle the hourly chime.

World Clock


The World Clock watch face looks similar to the Simple Clock watch face, but you’ll notice that at first launch the day of week indicators are blank. That’s because this watch face does not display the day of the week. Instead, you may customize these letters to display the name of a time zone of your choosing.

To customize this watch face, press and hold the Alarm button. The first letter in the top row will begin flashing. Press the Alarm button repeatedly to advance through the available letters in the first slot, then press the Light button to move to the second letter. Finally, press Light again to move to the time zone setting, and press Alarm to cycle through the available time zones. Press Light one last time to return to the world clock display.

Note that the second slot cannot display all letters or numbers. Also note that at this time, time zones do not automatically update for daylight saving time; you will need to manually adjust this field each spring and fall.

World Clock 2


This is an alternative world clock face that allows the user to cycle through a list of selected time zones. It extends the original implementation by Joey Castillo. The face has two modes: display mode and settings mode.

Settings mode

When the clock face is activated for the first time, it enters settings mode. Here, the user can select the time zones they want to display. The face shows a summary of the current time zone:

  • The top of the face displays the first two letters of the time zone abbreviation, such as “PS” for Pacific Standard Time or CE for “Central European Time”.
  • The upper-right corner shows the index number of the time zone. This helps avoid confusion when multiple time zones have the same two-letter abbreviation.
  • The main display shows the offset from UTC, with a “+” indicating a positive offset and a “-” indicating a negative offset. For example, the offset for Japanese Standard Time is displayed as “+9:00”.

The user can navigate through the time zones and select them using the following buttons:

  • The ALARM button moves forward to the next time zone, while the LIGHT button moves backward to the previous zone. This way, the user can cycle through all 41 supported time zones.
  • A long press on the LIGHT button selects the current time zone, and the signal indicator appears at the top left. Another long press of the LIGHT button deselects the time zone.
  • A long press on the ALARM button exits settings mode and returns to display mode.

Display mode

In the display mode, the face shows the time of the currently selected time zone. The face includes the following components:

  • The top of the face displays the first two letters of the time zone abbreviation, such as “PS” for Pacific Standard Time or “CE” for Central European Time.
  • The upper-right corner shows the current day of the month, which helps indicate time zones that cross the international date line with respect to the local time.
  • The main display shows the time in the selected time zone in either 12-hour or 24-hour form. There is no timeout, allowing users to keep the chosen time zone displayed for as long as they wish.

The user can navigate through the selected time zones using the following buttons:

  • The ALARM button moves to the next selected time zone, while the LIGHT button moves to the previous zone. If no time zone is selected, the face simply shows UTC.
  • A long press on the ALARM button enters settings mode and enables the user to re-configure the selected time zones.
  • A long press on the LIGHT button activates the LED illumination of the watch.



This is a recreation of the Wyoscan watch, which was a $175 watch in 2014. It was an f-91w pcb replacement.


8 frames per number * 6 numbers + the trailing 16 frames = 64 frames at 32 frames per second, this is a 2-second cycle time or 0.5 Hz.

It is giving me a stack overflow after about 2.5 cycles of the time display in the emulator, but it works fine on the watch.

I’d like to make something for the low energy mode, but I haven’t thought about how that might work, right now it just freezes in low energy mode until you press the 12-24HR button.

There are no controls; it simply animates as long as the page is active.

3 - Complications

In horology, a complication is an additional set of gears in a mechanical watch movenent that enables a secondary function, such as a sunrise/sunset dial. The watch faces in this category do just that.



The Activity face lets you record activities like you would do with a fitness watch. It supports different activities like running, biking, rowing etc., and for each recorded activity it stores when it started and how long it was.

You can save up to 99 activities this way. Every once in a while you can chirp them out using the watch’s piezo buzzer as a modem, then clear the log in the watch. To record and decode a chirpy transmission on your computer, you can use the web app here.

Using the face

When you activate the face, it starts with the first screen to select the activity you want to log.

  • ALARM cycles through the list of activities.
  • LONG ALARM starts logging.
  • While logging is in progress, the face alternates between the elapsed time and the current time.
  • You can press ALARM to pause (e.g., while you hop in to the baker’s for a croissant during your jog).
  • Pressing ALARM again resumes the activity.
  • LONG ALARM stops logging and saves the activity.

When you’re not loggin, you can press LIGHT to access the secondary faces.

  • LIGHT #1 => Shows the size of the log (how many activities have been recorded).
  • LIGHT #2 => The screen to chirp out the data. Press LONG ALARM to start chirping.
  • LIGHT #3 => The screen to clear the log in the watch. Press LONG ALARM twice to clear data.

Quirky details

The face will discard short activities (less than a minute) when you press LONG ALARM to finish logging. These were probably logged by mistake, and it’s better to save slots and chirping battery power for stuff that really matters.

The face will continue to record an activity past the normal one-hour mark, when the watch enters low energy mode. However, it will always stop at 8 hours. If an activity takes that long, you probably just forgot to stop logging.

The log is stored in regular memory. It will be lost when you remove the battery, so make sure you chirp it out before taking the watch apart.

See the top of activity_face.c for some customization options. What you most likely want to do is reduce the list of activities shown on the first screen to the ones you are regularly doing.



The Alarm face implements 16 customizable alarms on the sensor watch.


  • In normal mode, the alarm button cycles through all 16 alarms.
  • Pressing the alarm button long in normal mode toggles the corresponding alarm on or off.
    (Whereas pressing the alarm button extra long jumps back to the first alarm.)
  • Pressing the light button enters settings mode and cycles through the settings of each alarm.
    (Long pressing the light button enters settings mode without illuminating the led.)
  • In settings mode an alarm slot is selected by pressing the alarm button when the slot number in the upper right corner is blinking.
  • For each alarm slot, you can select the day. These are the day modes:
    • ED = the alarm rings every day
    • 1t = the alarm fires only one time and is erased afterwards
    • MF = the alarm fires Mondays to Fridays
    • WN = the alarm fires on weekends (Sa/Su)
    • MO to SU = the alarm fires only on the given day of week
  • You can fast cycle through hours or minutes by holding the alarm button.
  • You can select the tone in which the alarm is played. (Three pitch levels available.)
  • You can select how many “beep rounds” are played for each alarm. 1 to 9 rounds, plus extra long (‘L’) and extra short (‘o’) alarms.
  • The simple watch face indicates if any alarm is set within the next 24h by showing the signal indicator.



The Astronomy watch face is among the most complex watch faces in the Movement collection. It allows you to calculate the locations of celestial bodies in the sky, as well as distance in astronomical units (or, in the case of the Moon, distance in kilometers).

When you arrive at the Astronomy watch face, you’ll see its name (“Astro”) and an animation of two objects orbiting each other. You will also see “SO” (for Sol) flashing in the top left. The flashing letters indicate the currently selected celestial body. Short press Alarm to advance through the available celestial bodies:

  • SO - Sol, the sun
  • ME - Mercury
  • VE - Venus
  • LU - Luna, the Earth’s moon
  • MA - Mars
  • JU - Jupiter
  • SA - Saturn
  • UR - Uranus
  • NE - Neptune

Once you’ve selected the celestial body whose parameters you wish to calculate, long press the Alarm button and release it. The letter “C” will flash while the calculation is performed.

When the calculation is complete, the screen will display the altitude (“aL”) of the celestial body. You can cycle through the available parameters with repeated short presses on the Alarm button:

  • aL - Altitude (in degrees), the elevation over the horizon. If negative, it is below the horizon.
  • aZ - Azimuth (in degrees), the cardinal direction relative to true north.
  • rA - Right Ascension (in hours/minutes/seconds)
  • dE - Declination (in degrees/minutes/seconds)
  • di - Distance (the digits in the top right will display either aU for astronomical units, or K for kilometers)

Long press on the Alarm button to select another celestial body.

Blinky Light


The blinky light watch face was designed as a tutorial for making a watch face in Movement, but it actually might be useful to have a blinking light in a pinch.

The screen displays the name of the watch face (”BL”), as well as an S at the top right for slow blink or an F for fast blink. The bottom line selects the color: green, red or yellow. You can change the speed of the blinking light by pressing the Alarm button, and change the color with the Light button. A long press on the Alarm button starts the blinking light, and another long press stops it.

Note that this will chew through your battery! The green LED uses about 450µA at full brightness, which is 45 times the normal power consumption of the watch. The red LED is an order of magnitude less efficient (4500 µA), and the yellow setting lights both LEDs, which chews through nearly 5 milliamperes. This means that one hour of yellow blinking is likely to eat up between 2 and 3 percent of the battery’s usable life! Still, if you need to signal your location to someone in a dark forest, this watch face could come in handy.

Just try to use the green LED as much as you can.



Breathing is a complication for guiding boxed breathing sessions. Boxed breathing is a technique to help you stay calm and improve concentration in stressful situations.

Usage: Timed messages will cycle as long as this face is active. Press ALARM to toggle sound.



Slight extension of the original countdown face by Wesley Ellis.

  • Press the light button to enter setting mode and adjust the countdown timer.
  • Start and pause the countdown using the alarm button, similar to the stopwatch face.
  • When paused or terminated, press the light button to restore the last entered countdown.

Max countdown is 23 hours, 59 minutes and 59 seconds.

Note: we have to prevent the watch from going to deep sleep using movement_schedule_background_task() while the timer is running.



Counter face is designed to count the number of running laps during exercises.


  • Short-press ALARM to increment the counter (loops at 99)
  • Long-press ALARM to reset the counter.
  • Long-press LIGHT to toggle sound.



Displays some pre-defined data that you might want to remember Math constants, birthdays, phone numbers…

Usage: Edit the global variable pi_data in “databank_face.c” to the define the data that will be displayed. Each “item” contains a two-letter label (using the day-of-week display), then a longer string that will be displayed one “word” (six characters) at a time.

  • Short-press ALARM to display the next word.
  • Short-press LIGHT to display the previous word.
  • Long-press ALARM to display the next item.
  • Long-press LIGHT to display the previous item.

Day One


This watch face displays the number of days since a given date. It was originally designed to display the number of days you’ve been alive, but technically it can count up from any date in the 20th century or the 21st century, so far.

Long press on the Alarm button to enter customization mode. The text “YR” will appear, and will allow you to set the year starting from 1959. Press Alarm repeatedly to advance the year. If your birthday is before 1959, advance beyond the current year and it will wrap around to 1900. Once you have set the year, press Light to set the month (“MO”) and day (“DA”), advancing the value by pressing Alarm repeatedly.

Note that at this time, the Day One face does not display the sleep indicator in sleep mode, which may make the watch appear to be unresponsive in sleep mode. You can still press the Alarm button to wake the watch. This UI quirk will be addressed in a future update.

Disc Golf


Keep track of scores in discgolf or golf! The watch face operates in three different modes:

  • dg_setting: Select a course
    • Enter this mode by holding down the light button. The screen will display the label for the hole and the lowest score since last boot.
    • Press alarm to loop through the holes. Press the light button to make a selection. This will reset all scores and start a new game in dg_idle mode.
  • dg_idle: We’re playing a hole
    • This either shows your current score relative to par, or the score for a particular hole.
    • At the start of a game, press alarm to loop through the holes and leave it your starting hole. For optimal experience, play the course linearly after that
    • If you’re viewing the hole you’re supposed to be playing, the watch face will display your score relative to par.
    • Use the alarm button to view other holes than the one you’re playing, in which case the input score for that hole will be displayed, in case it needs changing.
    • Long press the alarm button to snap back to currently playing hole.
    • To input scores for a hole in this mode, press the light button.
  • dg_scoring: Input score for a hole
    • In this mode, if the score is 0 (hasn’t been entered during this round), it will blink, indicating we’re in scoring mode. Press the alarm button to increment the score up until 15, in which case it loops back to 0.
    • Press the light button to save the score for that hole, advance one hole
    • if you’re not editing an already input score, and returning to idle mode.

When all scores have been entered, the LAP indicator turns on. At that point, if we enter dg_setting to select a course, the score for that round is evaluated against the current lowest score for that course, and saved if it is better.

Dual Timer


Inspired by special ops and tactical trope targeted watches like the Nixon Regulus that feature two chronographs for timing two simultaneous events, here is a watch face that expands upon Andreas Nebinger’s Stock Stopwatch Face code to implement this functionality.

  • ALARM starts/stops timer A, resets on the next start
  • LIGHT starts/stops timer B, resets on the next start

When a timer is running, tapping MODE toggles between displaying timers A or B, as indicated at the top of the display.

The currently selected timer shows minutes, seconds, and 100ths of seconds until the timed event passes the hour mark. Then it shows hours, minutes, and seconds. Once it runs for more than a day it shows days, hours, and minutes. The blinking colon indicates that the timer is running.

The longest time span the timers are able to track as 99 days and 23:59:59:99 hours and they will simply stop.

If the other timer that is not currently selected is also running then a plus sign is blinking next to the A or B indicator. Its progress is indicated by showing the timer’s currently highest time unit ( 100ths of seconds if less than a second, seconds if less than a minute, minutes if less than an hour, hours if less than a day, days if more than a day).

Please Note: If at least one timer is running then the default function of the MODE button to move to the next watch face is disabled to be able to use it to toggle between the timers. In this case LONG PRESSING MODE will move to the next face instead of moving back to the default watch face.

IMPORTANT: This watch face uses the same TC2 callback counter as the Stock Stopwatch watch-face. It works through calling a global handler function. The two watch-faces therefore can’t coexist within the same firmware. If you want to compile this watch-face then you need to remove the line <../watch_faces/complication/stock_stopwatch_face.c > from the Makefile.



A flashlight for use with the Flashlight sensor board.

When the watch face appears, the display will show “FL” in the top two positions. Pressing the Light button will toggle the flashlight on and off.



A simple and straightforward watch face for the ancient Eastern geomantic divination system of I Ching and the western system of “Geomancy”. It is an optional addition to the Toss Up Face.

The LIGHT button toggles between the two systems of geomancy.

The ALARM button casts an I Ching hexagram or Geomantic figure based on drawing virtual stalks from the True Random Number Generator in the Sensor Watch.

The figures are flipped 90 degrees clockwise, so the left side is the bottom and the right side the top.

LONG PRESSING ALARM toggles the display of the King Wen sequence index for the cast I Ching Hexagram (https://en.wikipedia.org/wiki/King_Wen_sequence )or the abbreviated name for the cast Geomantic Figure:

  • GF - Greater Fortune (Fortuna Major)
  • LF - Lesser Fortune (Fortuna Minor)
  • PO - Populus
  • VI - Via
  • AL - Albus
  • CO - Conjunctio
  • PA - Puella
  • AM - Amissio
  • PR - Puer
  • RU - Rubeus
  • AQ - Acquisitio
  • LA - Laetitia
  • TR - Tristitia
  • CA - Carcer
  • HD - Head of the Dragon (Caput Draconis)
  • TD - Tail of the Dragon (Cauda Draconis)



Allows the user to record a single succesful instance of a particular habit occuring per day, and displays history for eight days prior as well as a total counter.



The Interval face provides 9 customizable interval timers, which can be used for hit training and/or time management techniques.

  • To cycle through the 9 interval timers, press the alarm button (short press). For each timer slot, the relevant details for each timer phase are shown in a “carousel” (see below).
  • To start an interval timer, press and hold the alarm button.
  • To pause a running timer, press the alarm button (short press).
  • To completely abort a running timer, press and hold the alarm button.
  • Press and hold the light button to enter settings mode for the current interval timer. Short pressing the light button cycles through the settings of each timer.
  • Each interval timer has 1 to 4 phases of customizable length like so:
    (1) prepare/warm up --> (2) work --> (3) break --> (4) cool down

When setting up or running a timer, each of these phases is indicated by the letters “PR” (prepare), “WO” (work), “BR” (break), or “CD” (cool down).

  • Each of these phases is optional, and you can set the corresponding minutes and seconds to zero. If you want to use the timer, at least one phase needs to be set to a non-zero value.
  • You can define the number of rounds either only for the work phase and/or for the combination of work + break phase. Let’s say you want an interval timer that counts 3 rounds of 30 seconds work, followed by 20 seconds rest, like so:
    work 30s –> work 30s –> work 30s –> break 20s
    You can do this by setting 30s for the “WO"rk phase and setting a 3 in the lower right-hand corner of the work page. The “LAP” indicator lights up at this position, to explain that we are setting laps here. After that, set the “BR"eak phase to 20s and leave the rest as it is.
  • If you want to set up a certain number of “full rounds”, consisting of work phase(s) plus breaks, you can do so at the “BR"eak page. The number in the lower right-hand corner determines the number of full rounds to be counted. A “-” means that there is no limit, and the timer keeps alternating between work and break phases.
  • This watch face comes with several pre-defined interval timers suitable for HIIT training (timer slots 1 to 4) as well as doing work according to the Pomodoro technique (timer slots 5 to 6). Feel free to adjust the timer slots to your own needs (or completely wipe them).



The Invaders watch face is an authentic remake of the “famous” number invaders game, found on the Casio calculator wristwatches CA-85 or CA-851.

How to play:

  • Press the alarm button to start the game. “Invaders” (just digits, tbh) will start coming in from the right-hand side.
  • Press the light button to “aim”. The digit on the top of the display cycles from 0 to 9.
  • If your aiming digit is identical to one of the invaders, press the alarm button to “shoot”. The corresponding invader will disappear.
  • If the invaders reach beneath the very first position, you loose one defense line. When all three defense lines are gone, the game is over.
  • Also: If you shoot more than 29 times per wave, you lose the game.
  • There are 16 invaders per wave. There is a short break between waves.
  • Long pressing the light button toggles sound on or off (not while playing).

The “n” invaders are ufos!

Whenever the sum of all invaders shot is divisible by 10 the next invader will be an ufo, represented by the n-symbol. Shooting a ufo gets you extra points. Example: shoot 2, 5, 3 –> ufo next

As for points: the earlier you shoot an invader, the more points you get.

To anyone interested in the original game manual, see here: https://www.digitalwatchlibrary.com/images/casio_manuals/0134.pdf

Moon Phase


The Moon Phase face is similar to the Sunrise/Sunset face: it displays the current phase of the moon, along with the day of the month and a graphical representation of the moon on the top row.

This graphical representation is a bit abstract. The segments that turn on represent the shape of the moon, waxing from the bottom right and waning at the top left. A small crescent at the bottom right will grow into a larger crescent, then add lines in the center for a quarter and half moon. All segments are on during a full moon. Then gradually the segments at the bottom right will turn off, until all that remains is a small waning crescent at the top left.

All segments turn off during a new moon.

On this screen you may press the Alarm button repeatedly to move forward in time: the day of the month at the top right will advance by one day for each button press, and both the text and the graphical representation will display the moon phase for that day. Try pressing the Alarm button 27 times now, just to visualize what the moon will look like over the next month.

Morse Calculator


Morse-code-based RPN calculator

The calculator is operated by first composing a token in Morse code, then submitting it to the calculator. A token specifies either a calculator operation or a float value.

These two parts of the codebase are totally independent:

  1. The Morse-code reader (mc.h, mc.c)
  2. The RPN calculator (calc.h, calc.c, calc_fn.h, calc_fn.c, small_strtod.c)

The user interface (morsecalc_face.h, morsecalc_face.c) lets you talk to the RPN calculator through Morse code.


  • light is dash
  • alarm is dot
  • mode is “finish character”
  • long-press mode or submit a blank token to switch faces
  • long-press alarm to show stack
  • long-press light to toggle the light

Morse code token entry

As you enter .s and -s, the morse code char you’ve entered will appear in the top center digit. At the top right is the # of morse code ./- you’ve input so far. The character resets at the 6th ./-.

Once you have the character you want to enter, push mode to enter it.

The character will be appended to the current token, whose 6 trailing chars are shown on the main display. Once you’ve typed in the token you want, enter a blank Morse code character and then push mode. This submits it to the calculator.

Special characters:

  • Backspace is ( (-.--.).
  • Clear token input without submitting to calculator is Start transmission (-.-.-).

Writing commands

First the calculator will try to interpret the token as a command/stack operation. Commands are defined in calc_dict[] in movement/lib/morsecalc/calc_fns.h. If the command doesn’t appear in the dictionary, the calculator tries to interpret the token as a number.

Writing numbers

Numbers are written like floating point strings. Entering a number pushes it to the top of the stack if there’s room. This can get long, so for convenience numerals can also be written in binary with .- = 01.

0   1    2    3    4    5    6    7    8    9
.   -    -.   --   -..  -.-  --.  ---  -... -..-
e   t    n    m    d    k    g    o    b    x
  • Exponent signs must be entered as “p”.
  • Decimal place “.” can be entered as “h” (code ….)
  • Sign “-” can be entered as “Ch digraph” (code —-)

For example: “4.2e-3” can be entered directly, or as “4h2pC3” similarly, “0.0042” can also be entered as “eheedn” Once you submit a number to the watch face, it pushes it to the top of the stack if there’s room.

Number display

After a command runs, the top of the stack is displayed in this format:

  • Main 4 digits = leading 4 digits
  • Last 2 digits = exponent
  • Top middle = [Stack location, Sign of number]
  • Top right = [Stack exponent, Sign of exponent]

Blank sign digit means positive. So for example, the watch face might look like this:

[   0 -5]
[4200 03]

… representing +4.200e-3 is in stack location 0 (the top) and it’s one of five items in the stack.

Looking at the stack

To show the top of the stack, push and hold light/alarm or submit a blank token by pushing mode a bunch of times. To show the N-th stack item (0 through 9):

  • Put in the Morse code for N without pushing the mode button.
  • Push and hold alarm.

To show the memory register, use m instead of a number.

To see all the calculator operations and their token aliases, see the calc_dict[] struct in calc_fns.h



The Orrery watch face is similar to the Astronomy watch face in that it calculates properties of the planets, but instead of calculating their positions in the sky, this watch face calculates their absolute locations in the solar system. This is only useful if you want to plot the planets on graph paper, but hey, you never know!

The controls are identical to the Astronomy watch face: while the title screen (“Orrery”) is displayed, you can advance through the available planets with repeated short presses on the Alarm button. The available planets:

  • ME - Mercury
  • VE - Venus
  • EA - Earth
  • LU - Luna, the Earth’s moon
  • MA - Mars
  • JU - Jupiter
  • SA - Saturn
  • UR - Uranus
  • NE - Neptune

Note that the sun is not available in this menu, as the sun is always at (0,0,0) in this calculation.

Long press on the Alarm button to calculate the planet’s location, and after a flashing “C” (for Calculating), you will be presented with the planet’s X coordinate in astronomical units. Short press Alarm to cycle through the X, Y and Z coordinates, and then long press Alarm to return to planet selection.

The large numbers represent the whole number part, and the two smaller numbers (in the seconds place) represent the decimal portion. So if you see “SA X 736” and “SA Y -662”, you can read that as an X coordinate of 7.36 AU and a Y coordinate of -6.62 AU. You can literally draw a dot at (0, 0) to represent the sun, and a dot at (7.36, -6.62) to represent Saturn. (the Z coordinates tend to be pretty close to zero, as the planets largely orbit on a single plane, the ecliptic)

Planetary Hours



Both the 24 hour day and the order of our weekdays have quite esoteric roots. The ancient Egyptians divided the day up into 12 hours of sunlight and 12 hours of night time. Obviously the length of these hours varied throughout the year.

The Greeks assigned each hour a ruler of the planetary gods in the ancient “Chaldean” order from slowest (Chronos for Saturn) to fastest (Selene for Moon). Because 24 hours cannot be equally divided by seven, the planetary rulers carried over to the first hour of the next day, effectively ruling over the entire day and lending the whole day their name. The seven day week was born.


This complication watch face displays the start time of the current planetary hour according to the given location and day of the year. The number of the current planetary hour (1 - 24) is indicated at the top right.

Short pressing the ALARM button flips through the start times of the following planetary hours, long pressing it flips backwards in time. A long press of the LIGHT button immediately switches back to the start time of the current hour. The Bell indicator always marks the current planetary hour in the list. The LAP indicator shows up when the hours of the next phase are part of the upcoming day instead of the current one. This happens when the watch face is launched after sunset.

The planetary ruler of the current hour and day is displayed at the top in Latin or Greek shorthand notation:

  • Saturn (SA) / Chronos (CH) / ♄
  • Jupiter (JU) / Zeus (ZE) / ♃
  • Mars (MA) / Ares (AR) / ♂
  • Sol (SO) / Helios (HE) / ☉
  • Venus (VE) / Aphrodite (AF) / ♀
  • Mercury (ME) / Hermes (HR) / ☿
  • Luna (LU) / Selene (SE) / ☾

A short press of the LIGHT button toggles between Latin and Greek ruler shorthand notation.

(IMPORTANT: Make sure the watch’s time, timezone and location are set correctly for this watch face to work properly!)

Planetary Time



Both the 24 hour day and the order of our weekdays have quite esoteric roots. The ancient Egyptians divided the day up into 12 hours of sunlight and 12 hours of night time. Obviously the length of these hours varied throughout the year.

The Greeks assigned each hour a ruler of the planetary gods in the ancient “Chaldean” order from slowest (Chronos for Saturn) to fastest (Selene for Moon). Because 24 hours cannot be equally divided by seven, the planetary rulers carried over to the first hour of the next day, effectively ruling over the entire day and lending the whole day their name. The seven day week was born.


The hour digits of this complication watch-face display the current planetary hour according to the given location and day of the year (First hour from 12am to 1am, the second hour from 1am to 2am, and so forth).

Like with normal clocks the minutes and seconds help dividing the hour into smaller units. On this watch-face, all units naturally vary in length because the planetary hours are not fixed by duration but by the moments of sunrise and sunset which obviously vary throughout the year, especially in higher latitudes.

On this watch-face the hours indicated as 12am to 12pm (00:00 - 12:00) are used for the planetary daytime hours between sunrise and sunset and hours indicated as 12pm to 12am (12:00 - 00:00) are used for the planetary night hours after sunset and before sunrise.

The planetary ruler of the current hour and day is displayed at the top in Latin or Greek shorthand notation:

  • Saturn (SA) / Chronos (CH) / ♄
  • Jupiter (JU) / Zeus (ZE) / ♃
  • Mars (MA) / Ares (AR) / ♂
  • Sol (SO) / Helios (HE) / ☉
  • Venus (VE) / Aphrodite (AF) / ♀
  • Mercury (ME) / Hermes (HR) / ☿
  • Luna (LU) / Selene (SE) / ☾

The ALARM button toggles between displaying the ruler of the hour and the ruler of the day

The LIGHT button toggles between Latin and Greek ruler shorthand notation

(IMPORTANT: Make sure the watch’s time, timezone and location are set correctly for this watch face to work properly!)



This face is a dice-rolling random number generator. Supports dice with 2, 4, 6, 8, 10, 12, 20, or 100 sides.

Press LIGHT to cycle through die type. The current die size is indicated on the left (“C” for 100)

Press ALARM to roll the selected die.



The Pulsometer is an implementation of a sort of a classic mechanical watch complication. A classic pulsometer complication involves a chronograph with a scale calibrated for counting a certain number of heartbeats (often 30). You start it and begin counting heartbeats, and stop it after counting the specified number of beats. Once stopped, the needle will point to your heart rate.

The pulsometer on Sensor Watch flashes its instructions at launch: “Hold Alarm + count 30 beats.” Using the hand on the side where you wear your watch, touch your carotid artery (in your neck) and feel for your pulse. Once you find it, use your other hand to press and hold the Alarm button, and count your heartbeats. When you reach 30 beats, release the Alarm button. The display will show a number such as “60 bpm”; this is your heart rate in beats per minute.

Two notes:

  1. For the first few seconds of a measurement, the display will read “Hi”. This indicates that it’s too early for the measured value to be a valid heart rate. Once the measurement is below 240 bpm, the display will update.
  2. If you hold the button down for more than 45 seconds, the display will read “Lo”. If it took this long for you to count 30 heartbeats, this indicates that your heart rate is below 40 beats per minute.



Randonauting is a way to turn the world around you into an adventure and get the user outside of their day-to-day routine by using a random number generator to derive a coordinate to journey to. In Randonauts lore so-called “Blind Spots” are places you cannot reach methodologically. They may exist in your own backyard for your whole life and you will never even notice them, because you simply have no reason to go to that exact place or look in its direction. Since the very limitations of our behavioral algorithms are the reason for the existence of blindspots, they can only be found using a randomizer.

This watch face generates a random location based on the watch’s location and a set radius using the official Randonautica Blind Spot algorithm.

The ALARM button starts the random location generation and then automatically displays the found Blind Spot.

By pressing ALARM again the user can flip through different pieces of information about the Blind Spot: Distance (DI), Bearing Degree (BE), Latitude degrees and decimal digits (LA), Longitude degrees and decimal digits (LO).

Pressing LIGHT switches between generating a new blind spot (“Rando”) and displaying the info of the last generated one (“Point”).

LONG PRESSING LIGHT toggles setup mode. Here pressing LIGHT switches between setting the desired radius (RA) and setting the random number generator (RNG) for generating the blind spot.

ALARM changes the values respectively:

  • The radius can be set in 500 meter steps between 1000 and 10,000 meters
  • The RNG can be set to “true” which utilizes the SAML22J’s internal True Random Number Generator
  • Setting it to “psudo” will use the pseudorandom number generation algorithm arc4random
  • Setting it to “chance” will randomly chose either of the RNGs for each generation (default)

LONG PRESSING ALARM toggles DATA mode in which the currently generated Blind Spot coordinate can be written to the <place.loc> file on the watch (press ALARM) and set as active high precision location used by other watch faces. It does not overwrite the low precision location information in the watch register commonly used for astronomical watch faces.

Rate Meter


The rate meter shows the rate per minute at which the ALARM button is being pressed. This is particularly useful in sports where cadence tracking is useful. For instance, rowing coaches often use a dedicated rate meter - clicking the rate button each time the crew puts their oars in the water to see the rate (strokes per minute) on the rate meter.

RPN Calculator


The calculator uses RPN notation. So instead of using infix operators, the operators always follow the parameters.

Example: To calculate 4 - 3 one would enter 4 3 -

Using this notation also does not require any braces, so instead of 2 * (3 - 2) one would enter 2 3 2 - *.

The parameters are put on to a stack, which currently has a size of 4. So if one enters 2 3 2 - * the stack would contain 2 3 2 0. The subtraction then uses the first two values from the stack and pushes the result back on the stack, which leaves 1 2 0 0. The multiplication then uses the next two values from the stack and pushes the end result: 2 0 0 0.

Normal mode

In normal mode the top of the stack is displayed (initially zero), which usually represents the result of the calculation.

  • ALARM enters number mode
  • LIGHT enters operator mode
  • MODE switches to the next watch face

Number mode

Number mode pushes a new parameter on the stack. The first four digits are whole numbers, the last two (smaller) digits are decimals.

  • LIGHT cycles through digits
  • ALARM increases the selected digit
  • MODE pushes the parameter on the stack (and goes back to normal mode)

Operation mode

Operation mode executes operations on the stack. Parameters are taken from the stack and the result is pushed back. If there aren’t enough parameters on the stack, the calculator will go into error mode.

The display shows the current selected operation.

  • LIGHT cycles through the available operations
  • ALARM executes the selected operation (and goes back to normal mode, which will display the result)

Currently implemented operations:

  • add (2 params)
  • sub (2 params)
  • mul (2 params)
  • div (2 params)
  • pow (2 params)
  • sqrt (1 param)
  • pi (0 params, will just push pi onto the stack)

Error mode

An error has happened (currently only caused by too few parameters on the stack).

  • ALARM goes back to normal mode
  • MODE switches to the next watch face


To calculate the following equation:

2 * (3 - 2)

which would be the following in RPN notation:

2 3 2 - *

the following button presses are needed:

  • ALARM enter number mode
  • ALARM 1
  • ALARM 2
  • MODE push number, back to normal mode
  • ALARM enter number mode
  • ALARM 1
  • ALARM 2
  • ALARM 3
  • MODE push number, back to normal mode
  • ALARM enter number mode
  • ALARM 1
  • ALARM 2
  • MODE push number, back to normal mode
  • LIGHT enter operation mode
  • LIGHT change operation to sub
  • ALARM execute sub, back to normal mode
  • LIGHT enter operation mode
  • LIGHT change operation to mul
  • ALARM execute mul, back to normal mode

RPN Calculator Alternate


Operations appear in the ‘day’ section; ALARM changes between operations when operation is flashing. LIGHT executes current operation.

This is the alternate face because it has a non-traditional number entry system which I call ‘guess a number’. In number entry mode, the watch tries to guess which number you want, and you respond with ‘smaller’ (left - MODE) or larger (right - ALARM). This means that when you are entering a number, MODE will no longer move between faces!

Example of entering the number 27

  • select the NO operation (probably unnecessary, as this is the default), and execute it by hitting LIGHT.
  • you are now in number entry mode; you know this because nothing is flashing.
  • Watch displays 10; you hit ALARM to say you want a larger number.
  • Watch displays 100; you hit MODE to say you want a smaller number.
  • Continuing: 50 -> MODE -> 30 -> MODE -> 20 -> ALARM -> 27
  • Hit LIGHT to add the number to the stack (and now ‘NO’ is flashing again, indicating you’re back in operation selection mode).

One other thing to watch out for is how quickly it will switch into scientific notation due to the limitations of the display when you have large numbers or non-integer values. In this mode, the ‘colon’ serves at the decimal point, and the numbers in the top right are the exponent.

As with the main movement firmware, this has the concept of ‘secondary’ functions which you can jump to by a long hold of ALARM on NO. These are functions to do with stack manipulation (pop, swap, dupe, clear, size (le)). If you’re not on NO, a long hold will take you back to it.

See ‘functions’ in “rpn_calculator_alt_face.c” for names of all operations.



Implements a sailing timer.

Waiting mode:

LIGHT button enters settings ALARM button starts the timer (sailing mode).

Sailing mode:

ALARM button switches to next programmed start signal. Long press on LIGHT button resets timer and enters waiting mode. Countdown to zero, then switch to counting mode.

Counting mode:

After the start signal (0s), the duration of the race is counted (like a stopwatch timer). ALARM button increases the lap counter, ALARM long press resets lap counter. Long press on LIGHT button resets timer and enters waiting mode.

Setting mode:

ALARM button increases active (blinking) signal. Goes to 0 if upper boundary (11 or whatever the signal left to the active one is set to) is met. 10 is printed vertically (letter o plus top segment). ALARM button long press resets to default minutes (5-4-1-0). LIGHT button cycles through the signals. Long press on LIGHT button cycles through sound modes:

  • Bell indicator: Sound at start (0s) only.
  • Signal indicator: Sound at each programmed signal and at start.
  • Bell+Signal: Sound at each minute, at 30s and at 10s countdown.
  • No indicator: No sound.

Ship’s Bell


A ship’s bell complication.

Similar to the default hourly signal of the simple_clock_face this complication will use the buzzer to signal the time in half-hour intervals according to the scheme mentioned above.

Additionally, the user can specify one of the three watches of the standard merchant watch system to only receive signals during this watch.

If no watch is specified all signals are emitted.


  • short press Alarm button: Turn on/off bell
  • long press Alarm button: Cycle through the watches (All/1/2/3)

Stock Stopwatch


The Stock Stopwatch face implements the original F-91W stopwatch functionality, including counting hundredths of seconds and lap timing.

  • Use the alarm button to start and stop the stopwatch.
  • Press the light button while the stopwatch is running to view the lap time. The stopwatch continues running in the background, indicated by a blinking colon.
  • Press the light button again to switch back to the running stopwatch.
  • Press the light button when the timekeeping is stopped to reset the stopwatch.

There are two improvements compared to the original F-91W:

  1. When the stopwatch reaches 59:59, the counter does not simply jump back to zero but keeps track of hours in the upper right-hand corner (up to 24 hours).
  2. Long-press the light button to toggle the LED behavior. It either turns on with each button press or remains off.



The Stopwatch face provides basic stopwatch functionality: you can start and stop the stopwatch with the alarm button. Pressing the light button when the timer is stopped resets it. This face does not count sub-seconds.



This watch face displays local sunrise and sunset times. During the day, it displays today’s sunset; at night, it displays tomorrow’s sunrise.

When you first see this watch face, it will display “No Loc”, or No Location. This is because your latitude and longitude are required to calculate sunrise and sunset. When on this screen, you can set your location in a similar way to the World Clock screen.

Press and hold Alarm to enter location setting mode. The top line will read “LA” (Latitude), and the bottom line “+ 0000”. The large digits are the whole number part of the latitude, and the smaller digits (in the seconds place) are the fractional part. Enter your latitude and longitude (“LO”) by pressing the Alarm button to change the sign or advance the digits, and the Light button to move to the next character; for example, a latitude of 40.73° N would be “+ 4073”, and a longitude of 73.94° W would be “–07394”.

Once you have set your latitude and longitude, the Sunrise/Sunset face will display the next sunrise or sunset on the bottom row, and the day of that sunrise or sunset at the top right.

A short press on the Alarm button will advance to the following sunrise or sunset: for example, on Monday afternoon, it will display Monday evening’s sunset, but a short press on the Alarm button will display Tuesday morning’s sunrise.

If you made a mistake while entering your location, or if you simply wish to change your location, you can re-enter location setting mode with another long press on the Alarm button.



The Tachymeter complication emulates the tachymeter function often present in watches, that computes the average speed in [units per hour] for a given distance given in [units].

Use case:

  • User sets the distance
  • User starts the tachymeter when the trip begins
  • User stops the tachymeter when the trip ends
  • The watch presents the average speed and trip duration in seconds


  • Go to tachymeter face, TC is shown in the Weekday Digits
  • A steady d in the Day Digits indicates the distance to be used. To edit the distance:
    • Long-press the Alarm button, the distance edition page (d will blink)
    • Use the Light button to change the editing (blinking) digit, and press Alarm to increase its value
    • Once done, long-press the Alarm button to exit the distance edition page
  • Press the Alarm button to start the tachymeter.
    • A running animation will appear in the Day Digits
  • Press the Alarm button to stop the tachymeter
    • The average speed and total time information will alternate.
    • The average speed will be shown alongside /h in the Day Digits; and the total time will be shown alongside t in the Day Digits.
  • Long press the Light button to return to the distance d page, and restart the tachymeter from there.
  • Long-press the light button in the steady distance page to reset the distance to 1.00

Pending design points

  • movement_request_tick_frequency(4) is used to obtain a 4Hz ticking, thus having a time resolution of 250 ms. Not sure if using event.subsecond` is the proper way to get the fractions of second for the start and final times.
  • For distance and average speed, the Second Digits (position 8 and 9) can be seen as decimals, thus possible to show distances as short as 0.01 km (or miles) and speeds as low as 0.01 km/h (or mph). However, if the same idea is used for the total time (showing hundredths), this limits the display to 9999.99 seconds (~2h:45m).



Tally face is designed to act as a tally counter. Based on the counter_face watch face by Shogo Okamoto.

To advance the counter, press the ALARM button. To reset, long press the ALARM button.



Draw from a deck of tarot cards. Can choose between major arcana only or entire deck.

In tarot reading, a card orientation can be upright or inverted, and the interpertation of the card can change depending on this state. This face lights the alarm indicator to show when a card is inverted. Just ignore it if you prefer not to deal with card inversions.

This face uses the terms “Wands”, “Cups”, “Swords” and “Coins” for the four suits, and numbers to represent the 14 ranked cards, with the cards 11-14 representing the Page, the Knight, the Queen, and King respectively.

Default draw is a 3-card major arcana spread.

To make it easier to keep track of where you are in the list of drawn cards, after drawing, “St” is shown for the 1st card in the spread and “En” is shown for the last card.

At any point, the mode button can be held to return to your first configured watch face.

When “Major” or “All” is shown:

  • Light button: cycle # of cards to draw
  • Light button (long press): toggle between major arcana and all cards
  • Alarm button: shuffle deck and draw cards

After cards are drawn/showing:

  • Light button: view the next drawn card
  • Alarm button: shuffle and re-draw new cards
  • Light button (long press): go back to Draw screen, for choosing different draw parameters.

Temperature Chart


Gathers temperature statistics in a chart form. Statistics bins are per hour / per 0.5°C.

Saved to file every day at 00:00. Can help improve watch precision in the future.

If you can gather statistics over few months, and then send “tempchart.ini” to 3@14.by, it will help future generations of precision quartz watches.

Time Left


The Time Left Face helps you visualize how far you have progressed in a certain time span. Similar to the Day One Face, you can set your starting date. Additionally, you can also set your target or destination date. You can then use the face to display your progress in various ways.


  • Long-pressing of the light button starts the settings mode:

    • First, you set the beginning date (indicated by a ‘b’ in the upper right corner).
    • Begin by setting the year (indicated by the letter ‘YR’). Use the alarm button to cycle through the values. Short-pressing the light button brings you to the next settings page.
    • Set the values in this order:
      1. beginning date (indicated by a ‘b’): year - month - day
      2. destination date (indicated by a ’d’): year - month - day
    • After cycling through all settings pages, the face returns to display mode.
  • In display mode, use the alarm button (short press) to cycle through these four types of display:

    1. number of days left (‘DL’) until the destination date is reached.
    2. remaining days expressed as a percentage of the total time span. The value is shown with two decimals, using the colon as a decimal point.
    3. number of days passed (‘DA’) since the beginning date. (This is the same value the Day One Face would give you.)
    4. number of days passed expressed as a percentage of the total time span.

What is this for?

You can use this watch face to be reminded of any kind of progress between a set start and end date. The brave among us can use it as a kind of memento mori visualization. Set your date of birth and look up the average life expectancy of your age cohort based on publicly available mortality tables. Then, set the statistically expected day of death as the target date, and you will be able to see how much of your time has passed and how much is still to come.



The timer watch face is an advanced countdown face, providing the functionality of starting a countdown by choosing one out of nine programmable timer presets. A timer/countdown can be 23 hours, 59 minutes, and 59 seconds max. A timer can also be set to auto-repeat, which is indicated by the lap indicator.

How to use in NORMAL mode:

  • Short-pressing the alarm button cycles through all preset timer lengths. Find the current timer slot number in the upper right-hand corner.
  • Long-pressing the alarm button starts the timer.
  • Long-pressing the light button initiates settings mode.

How to use in SETTINGS mode:

  • There are up to nine slots for storing a timer setting. The current slot is indicated by the number in the upper right-hand corner.
  • Short-pressing the light button cycles through the settings values of each timer slot in the following order:
    hours -> minutes -> seconds -> timer repeat
  • Short-pressing the alarm button alters the current settings value.
  • Long-pressing the light button returns to normal mode.

Tomato Productivity Timer


Add a “tomato” timer watch face that alternates between 25 and 5 minute timers as in the Pomodoro Technique.

The top right letter shows mode (f for focus or b for break). The bottom right shows how many focus sessions you’ve completed. (You can reset the count with a long press of alarm)

When you show up and it says 25 minutes, you can start it (alarm), switch to 5 minute (light) mode or leave (mode).

When it’s running you can reset (alarm), or leave (mode).

When it’s done, we beep and go back to step 1, changing switching mode from focus to break (or break to focus)

Toss Up


Playful watch face for games of chance or divination using coins or dice.

LIGHT switches between Coins and Dice mode


ALARM tosses a coin. If it lands on heads it gets sorted to the left side of the display, if it lands on tails then sorted to the right side.

LONG PRESSING ALARM adds up to 5 more coins to the toss for more nuance in the decision making (e.g. three heads vs two tails could be read as “yes, but with serious doubts”).

LONG PRESSING LIGHT flips through additional style for the coins from the default Ө/O to H/T (heads/tails), Y/N (yes/no), E/Ǝ, C/Ↄ

LONG PRESSING ALARM on the “Coins” title page resets to one coin. LONG PRESSING LIGHT on the “Coins” title page resets the style to Ө/O


ALARM rolls a six sided dice.

LONG PRESSING ALARM adds up to 2 more dice to the roll.

LONG PRESSING LIGHT flips through other available polyhedral dice types with less or more than the default 6 sides. The options are D2, D4, D6, D8, D10, D12, D20, D24, D30, D32, D36, D48, and a hypothetical D99.

When more than one dice is used for a roll this changes only the last added dice. (see Note below)

LONG PRESSING ALARM on the “Dice” title page resets to one dice. LONG PRESSING LIGHT on the “Dice” title page resets the dice to D6.

Please Note: If you need let’s say a D8, D12, and D20 for your rolls then the procedure to set this up would be as follows: from the default screen where you can roll the one D6 dice you would LONG PRESS LIGHT a few times to change the D6 to a D8, then LONG PRESS ALARM to add a second dice, LONG PRESS LIGHT again until the second dice changes to D12, then LONG PRESS ALARM to add the third dice and LONG PRESS LIGHT again a few times until it becomes a D20.

TOTP Generator


This watchface generates time based one time passwords (two factor auth codes) allowing you to sign in securely to many popular websites (e.g. Google, GitHub). Time-based one-time password (TOTP) is a computer algorithm that generates a one-time password (OTP) that uses the current time as a source of uniqueness.

Press the Alarm button to cycle between your configured websites / TOTP secrets.

The watchface supports multiple websites / TOTP secrets, which need to be extracted from TOTP QR codes and added to the source code for the watchface as follows:

  1. Obtain a TOTP secret or QR ode from the website you want to generate codes for.
  2. If you have just the QR code, Stefan Sundin’s web site will allow you to extract the secret - it will be an alphanumeric string around 32 characters long, which is the TOTP secret encoded in Base32.
  3. To add the secret to the watchface code, you need to convert it to hexadecimal bytes. This cryptii.com page will allow you to do that conversion. Note you’ll have to enter your TOTP secret in uppercase. Shell tools can be used to convert secret to bytes:
  1. Finally, you’ll need to take the Hexadecimal bytes and add them to the TOTP watchface source code and recompile movement:

Edit totp_face.c

You may want to remove the demo keys. Assuming you want to add a key to the end of the list:

static const uint8_t num_keys = 2;

Add one to the number on this line.

static uint8_t keys[] = {
   // Add the hex bytes for your key

Add the hexadecimal bytes from step 3 to the end of this array, comma separated and each one preceeded by 0x. Don’t forget to add a comma after the previous final byte.

static const uint8_t key_sizes[] = {

Add the size of your secret (the number of hex bytes you just added) to the end of this array.

static const uint32_t timesteps[] = {

Add another 30 entry to the end of this array.

static const char labels[][2] = {

Add a label for your secret… E.g. if it’s for your Google account you might want to add { 'g', 'o' } as a friendly label.

That’s it - enjoy the convenience of TOTP codes on your wrist!

TOTP Generator LFS


Time-based one-time password (TOTP) generator using LFS

Reads from a file “totp_uris.txt”, containing a single secret key in a series of URLs. Each line is what’s in a QR code, e.g.:

  • otpauth://totp/Example:alice@google.com?secret=JBSWY3DPEHPK3PXP&issuer=Example
  • otpauth://totp/ACME%20Co:john.doe@email.com?secret=HXDMVJECJJWSRB3HWIZR4IFUGFTMXBOZ&issuer=ACME%20Co&algorithm=SHA1&digits=6&period=30

This is also the same as what Aegis exports in plain-text format. This face performs minimal sanitisation of input, however.

At the moment, to get the records onto the filesystem, start a serial connection and run:

  • echo otpauth://totp/Example:alice@google.com?secret=JBSWY3DPEHPK3PXP&issuer=Example > totp_uris.txt
  • echo otpauth://totp/ACME%20Co:john.doe@email.com?secret=HXDMVJECJJWSRB3HWIZR4IFUGFTMXBOZ&issuer=ACME%20Co&algorithm=SHA1&digits=6&period=30 >> totp_uris.txt (note the double “»”)

You may want to customise the characters that appear to identify the 2FA code. These are just the first two characters of the issuer, and it’s fine to modify the URI.

If you have more than one secret key, press ALARM to cycle through them.



WAKE daily alarm face

Basic daily alarm clock face. Seems useful if nothing else in the interest of feature parity with the F-91W’s OEM module, 593.

Also experiments with caret-free UI: One button cycles hours, the other minutes, so there’s no toggling between display and adjust modes and no cycling the caret through the UI.

  • LIGHT advances hour by 1
  • LIGHT long press advances hour by 6
  • ALARM advances minute by 10
  • ALARM long press cycles through signal modes (just one at the moment)

4 - Demo Faces

These watch faces demonstrate functionality of the watch, and aren’t generally watch faces you’d build into a working firmware.

Character Set


This watch face displays all of the characters in the Sensor Watch character set. You can advance from one character to the next with a short press of the Alarm button.

This watch face may be useful to watch face developers, in that it can help them to understand which characters will work in different positions.



This face demonstrates the chirpy-tx library. It is intended to help you include chirpy-tx in your own watch faces that need to transmit data out of the watch.

The face’s first screen lets you select from a few built-in transmissions:

SCALE cycles through frequencies in fixed increments. This is intended to collect and analyze audio samples from different watches. With this info it may be possible to improve chirpy-tx’s parameters like the frequencies it uses to make the method more robust.

SHORT is a small transmission that contains data taked from the activity_face.

LONG is a longer transmission that contains the first two strophes of a famous sea shanty.

Select the transmission you want with ALARM, the press LONG ALARM to chirp.

To record and decode a chirpy transmission on your computer, you can use the web app here.



This watch was designed for the Crowd Supply marketing team, so they could photograph the various functions of Sensor Watch. The Alarm button advances through static screens that simulate different watch faces.

This watch face may only be useful to you if you need to photograph Sensor Watch, i.e. for a blog post.

Frequency Correction


While active, this face generates a square-wave on pin A1 of the 9-pin connector. The output frequency is adjustable from 64 Hz to 0.5 Hz. Long-press ALARM to cycle through available frequencies.

This face also displays the value of the watch’s frequency-correction register. This setting varies from -127 to +127. Press LIGHT to increment or ALARM to decrement the setting.

Hello There


A simple demo that displays the word “Hello” and then the word “there”, on an endless loop. Press ALARM to pause or resume the animation.

LIS2DW Accelerometer Data Logger


This is an experimental watch face for logging data on the “Sensor Watch Motion Express” board. I will add more documentation for this watch face once this sensor board is more widely available.



This watch face is very simple and has no controls to speak of. It displays the battery voltage as measured by the SAM L22’s ADC.

Note that the Simple Clock watch face includes a low battery warning, so you don’t technically need to this watch face unless you want to track the battery level.

5 - Sensors

Sensor Watch is designed to display data from sensors. The watch faces in this category read sensor data and present it in a useful way.

Accelerometer Data Acquisition


TODO: Add description here, including controls.

Light Meter


Aperture-priority Light Meter Face

Tested with the “Q3Q-SWAB-A1-00 Temperature + Test Points + OPT3001” flexboard. This flexboard could use a revision:

  • The thermistor components should be moved west a mm or flipped to the backside to avoid stressing the flexboard against the processor so much.
  • The ’no connect’ pad falls off easily.


  • Trigger a measurement by long-pressing Alarm. Sensor integration is happening when the Signal indicator is on.

  • ISO setting can be cycled by long-pressing Light. During integration the current ISO setting will be displayed.

  • EV measurement in the top right: “LAP” indicates “half stop”. So “LAP -1” means EV = -1.5. Likewise “LAP 13” means EV = +13.5

  • Aperture in the bottom right: the last 3 main digits are the f-stop. Adjust this number in half-stop increments using Alarm = +1/2 and Light = -1/2.

  • Best shutter speed in the bottom left: the first 3 digits are the shutter speed. Some special chars are needed here: “-” = seconds, “h” = extra half second, “K” = thousands. “HI” or “LO” if there’s no shutter in the dictionary within 0.5 stops of correct exposure.

  • Mode long-press changes the main digits to show raw sensor lux measurements.

Temperature Display


This watch face is designed to work with either the Temperature + GPIO sensor board or the Temperature + Light sensor board. It reads the current temperature from the thermistor voltage divider on the sensor board, and displays the current temperature in degrees Celsius.

When the watch is on your wrist, your body heat interferes with an ambient temperature reading, but if you set it on a bedside table, strap it to your bike handlebars or place it outside of your tent while camping, this watch face can act as a digital thermometer for displaying ambient conditions.

The temperature sensor watch face automatically samples the temperature once every five seconds, and it illuminates the Signal indicator just before taking a reading.

Pressing the Alarm button toggles the unit display from Celsius to Fahrenheit. Technically this sets the global “Metric / Imperial” flag, so any other watch face that displays localizable units will display them in the system selected here.

Temperature Log


This watch face automatically logs the temperature once an hour, and maintains a 36-hour log of readings. This watch face is admittedly rather complex, and bears some explanation.

The main display shows the letters “TL” in the top left, indicating the name of the watch face. At the top right, it displays the index of the reading; 0 represents the most recent reading taken, 1 represents one hour earlier, etc. The bottom line in this mode displays the logged temperature.

A short press of the “Alarm” button advances to the next oldest reading; you will see the number at the top right advance from 0 to 1 to 2, all the way to 35, the oldest reading available.

A short press of the “Light” button will briefly display the timestamp of the reading. The letters at the top left will display the word “At”, and the main line will display the timestamp of the currently displayed data point. The number in the top right will display the day of the month for the given data point; for example, you can read “At 22 3:00 PM” as ”At 3:00 PM on the 22nd”.

If you need to illuminate the LED to read the data point, long press the Light button and release it.

Temperature Testing


This watch face is similar to the Temperature watch face, but it updates the temperature several times per second. You likely don’t need this watch face, but it is useful for testing the temperature sensor boards.

6 - Settings

The watch faces in this section relate to watch configuration.



FineTune face allows to align watch with sub-second precision in 25/250ms accuracy. Counts time since previous finetune, and allows to calculate & apply ppm correction for nanosec.

Best used in conjunction with the NANOSEC face.

For more information, refer to Calibration with Nanosec.



The goal of nanosec face is dramatic improvement of SensorWatch accuracy. Minimum goal is <60 seconds of error per year. Full success is if we can reach <15 seconds per year (<0.47ppm error).

Best used in conjunction with the FINETUNE face.

For more information, refer to Calibration with Nanosec.



Based on and expanded from the Sunrise/Sunset face. Outsourced the location setting functionality to its own face. Also serves as a converter between different coordinate notation formats.

With the LIGHT button each place coordinate can be shown and edited in 4 different display modes:

  1. Decimal Latitude and Longitude (WGS84) up to 5 decimal points
  2. Latitude and Longitude (WGS84) in traditional DD°MM’SS" notation
  3. Ten digit Open Location Code (aka. PlusCode) format
  4. Ten digit Geohash format

Using the ALARM button the user can flip through 2 pages of coordinate info to see the first and second sets of digits.

(please also refer to the notes on precision below)

Editing Mode

A LONG PRESS of the LIGHT button toggles editing mode for each of the selected notations.

In this mode LIGHT moves the cursor and ALARM changes the letter cycling through the available alphabet or numbers.

When OLC or Geohash display are edited, Digit Info mode is activated. It serves as a workaround for the limitation of how ambiguously alphanumeric characters are displayed on the main seven segment digits of the watch face ( S or 5, I or 1, U or W?).

The selected letter is also shown in the much easier to read alphanumeric 8 segment weekday digit above. In addition the ‘24H’ indicator is active when the selected digit represents a number and the ‘PM’ indicator for a letter.

A LONG PRESS of LIGHT saves the changes.

Coordinates are read or stored to both the traditional internal location register and a file on the LFS file system (“place.loc”). By default the Watch Face loads the coordinates from file when activated. If no file is present, the coordinates are loaded from the register. (please also see the notes on precision below)

Auxiliary Mode: Digit Info

A LONG PRESS of the ALARM button toggles Digit Info mode when OLC or Geohash display is active. (LAP indicator is on) It is a means of being able to see the detailed Digit Info as described above but without the risk of accidentally editing any of digits.

Both ALARM and LIGHT buttons can be used to flip through the letters.

Notes on Coordinate Precision

The common WGS84 Latitude and Longitude degrees naturally do not represent meters in distance on the ground. 1° Longitude on the equatorial line equals a width of 111.32 kilometers, but at 40° latitude further North or South it is approximately 85 kilometers wide. The closer to the poles the narrower (and more precise) the latitude degrees get.

The Sensor Watch’s traditional 16bit location register only stores latitudes and longitudes with two decimal points. That equals a longitudal precision of 36 arc seconds, or ~1111 meters at the equator - precise enough for astronomical calculations, but not if you want to store the location of let’s say a building.

Hence we propose the <place.loc> file that serves the same purpose, but with a precision of five decimal digits. That equals 0.04 arc seconds or 1.11 meters at the equator.

Please also note that the different notations of this watch face also have varying magnitudes of precision:

Format Notation Precision at Equator Precision at 67° N/S
2d. Decimal LatLon 29.98, 31.13 1111.320 m 435.125 m
5d. Decimal LatLon 29.97916, 31.13417 1.111 m 0.435 m
DMS LatLon N 29°58′45″, E 31°8′3″ 30.833 m 12.083 m
Open Location Code 7GXHX4HM+MM 13.875 m 13.875 m
Geohash stq4s3x1qu 1.189 m 0.596 m

Since all notations are internally converted into degrees with 5 decimal points, expect some rounding errors when editing or loading the coordinates in other notation formats.



The Preferences watch face allows you to configure various options on your Sensor Watch. Like all other screens, you advance the field you’re setting with the Light button, and advance its value with the Alarm button. The Preferences watch face labels each setting with a two-letter code on the top row; the following list describes each setting and their options:

CL - Clock mode. This setting allows you to select a 12-or 24-hour clock display. All watch faces that support displaying the time will respect this setting; for example, both Simple Clock, World Clock and Sunrise/Sunset will display the time in 24 hour format if the 24 hour clock is selected here.

BT - Button tone. This setting is only relevant if you installed the buzzer connector, and it toggles the beep when changing modes. If Y, the buzzer will sound a tone when Mode is pressed. Change to N to make the Mode button silent.

TO - Timeout. Sets the time until screens that time out (like Settings and Time Set) snap back to the first screen. 60 seconds is a good default for the stock firmware, but if you choose a custom firmware with faces that you’d like to keep on screen for longer, you can set that here.

LE - Low Energy mode. Sets the time until the watch enters its low energy sleep mode. Options range from 1 hour to 7 days, or Never. The more often Sensor Watch goes to sleep, the longer its battery will last — but you will lose the seconds indicator while it is asleep. This setting allows you to make a tradeoff between the device’s responsiveness and its longevity.

LT - Light. This setting has three screens:

  • The first lets you choose how long the LED should stay lit when the Light button is pressed. Options are 1 second, 3 seconds and 5 seconds, or “No LED” to disable the LED entirely.
  • The second screen, titled “blu”, sets the intensity of the blue LED. Values range from 0 (off) to 15 (full intensity)
  • The third screen, “red”, sets the intensity of the red LED, again from 0 to 15. On the last two screens, the LED remains on so that you can see the effect of mixing the two LED colors. On the Special Edition boards, you’ll have red, blue and a variety of shades of pink and purple to experiment with!

Time Set


The Time Set watch face allows you to set the time on Sensor Watch. Use the Light button to advance through the field you are setting, and the Alarm button to change the value in that field. The fields are, in order: Hour, Minute, Second, Year, Month, Day and Time Zone.

For features like World Clock and Sunrise/Sunset to work correctly, you must set the time to your local time, and the time zone to your local time zone. This allows Sensor Watch to correctly offset the time. This also means that when daylight savings time starts or ends, you must update both the time and the time zone on this screen.

Time Set Hackwatch


This is an extended version of set_time face which allow setting seconds precisely. To achieve that - press and hold alarm button few seconds before 00 and release exaclty as reference clock turns 00.

All settings can go up, or down (long alarm press).

The challenge is that SensorWatch display is delayed 0.5 seconds vs hardware RTC clock. It is caused by interrupts being generated by raising edge of counter. It means there is no way to precisely trigger at 0.5s, as events at different frequencies slightly mismatch. This watch face achieves this approximately by triggering at 15th out of 32Hz events.

If you are <30 seconds when setting seconds - you will stay in the same minute. Otherwise - you will go to next minute.

Note that changing anything will slightly delay subseconds counter. This is why this face sets seconds last to achiveve best precision. Still, best possible precision is achieved with finetune face.