Relativity

RelativityThey’re not time zones!

In addition to the normal time, Relativity shows what time it would be based on how much activity you’ve done. For example, if you’ve taken 7500 steps, Relativity will show 3 PM on the steps dial (assuming you’re active between 6 AM and 6 PM). Try to keep your activity time ahead of the actual time!

When you exercise hard, you can see the time on the activity dials move faster than normal time — up to 60× faster!

The lower left dial shows activity time based on how many calories you’ve burnt. Optionally, basal calories (ie, those you burn while inactive) can be subtracted. Long-touch the dial to swap between including basal calories and excluding them .

The lower right dial shows activity time based on steps, distance or active zone minutes (AZM). Long-touch the dial to change its mode.

After you’ve reached today’s activity goal, the corresponding dial shows you’re doing tomorrow’s exercise with a +1.

The top right dial shows the date. The short hand indicates the month, and the long hand indicates the day of the month.

If the dial hands are obscuring the values displayed below them, a quick touch of the screen will bring the values to the front for a few seconds.

Other features:

  • Always-On Display mode (on compatible watches)
  • many color options
  • stats popup (long-touch top of screen)

Relativity costs $1 USD + tax.

Get Relativity

Activity Time

The following sections describe how ‘activity time’ (the times shown on the lower dials) is calculated.

Steps, Distance and AZM

This is the easiest case to understand. Before and after your activity period (which you can change), Relativity assumes that you won’t take any steps (or cover any distance or achieve any AZM). However, during your activity period, Relativity assumes that should take steps at a constant rate so that you achieve your daily step goal at the end of the activity period. This is shown by the red ‘track’ line below.

Relativity Steps Graph.png

In reality, you’ll take steps at varying rates all throughout the day. This is shown by the jagged black ‘achievement’ line.

Let’s assume that the real time is 12 PM (mid-day). At this time, assume that you’ve taken 7500 steps. This is indicated on the graph above by the ‘achievement’ line passing through 7500 steps at 12 PM.

Now look directly across to the red ‘track’ line, to see where it reaches the same number of steps (7500). This happens at hour 15; ie, Relativity wouldn’t expect you to reach 7500 steps until 3 PM. Therefore, the time shown on the steps dial would be 3 PM. Because the real time is only 12 PM, this means you’re three hours ahead of schedule.

Since steps are only expected to be taken during your activity period, your activity time will always be within your activity period. For example, if you take 10,001 steps in a day (with a goal of 10,000), your activity time will be tomorrow morning, just after the start of tomorrow’s activity period.

Even though this example only discusses steps, the logic is exactly the same for distance and AZM.

Energy Excluding Basal  Relativity energy-

This is the next easiest case to understand.

You have a Basal Metabolic Rate (BMR). This is the rate at which your body burns energy (Calories) when you’re not doing anything; it’s the energy required simply to stay alive. When you’re active (eg, during exercise), you burn energy at a faster rate.

Your watch normally reports your energy achievement and goal including your BMR. This means that the expected ‘track’ rate is never zero, and that you’re burning calories even when inactive.

Relativity can subtract BMR from your goal, achievement and track. In this case, outside of your activity period, your ‘track’ line is horizontal (as it was when considering steps, above). Similarly, if you’re inactive, your ‘achievement’ line will be horizontal (as for steps). To see any energy progress, you actually have to do something.

Because of these adjustments, the energy- case is equivalent to the steps case described above. This even means that your activity time for energy- will always be within your activity period: if you exceed today’s goal, you’ll be burning tomorrow’s non-basal energy.

A nice feature of this mode is that, when the dial says that the time is the end of your activity period (by default, 6 PM), you’re guaranteed of reaching your daily goal even if it’s only mid-day and you sit around for the rest of the day!

Energy Including Basal Relativity energy+

Relativity Energy+ Graph.pngOutside of your activity period, your energy ‘track’ line rises at your BMR (ie, the minimum possible rate at which you can burn energy). At the end of the day (ie, midnight), the ‘track’ line should finally reach your goal. During the activity period, the track line increases at a greater (constant) rate.

Your ‘achievement’ line will never be horizontal. It should never be flatter than the ‘track’ line outside of your activity period, which represents your BMR.

Apart from those changes, the way that Relativity calculates your activity time in energy+ mode is the same; ie, the dial will indicate the time of day at which you were expected to have burnt as many calories as you actually have at the present time.

Because the ‘track’ line is never horizontal, the energy+ dial can indicate any time of day. For example, when you’re almost at your goal, the energy+ time will be almost midnight. When you’ve just exceeded your daily goal, the energy+ time will be just after midnight tomorrow morning.

Statistics Popup

You can see more statistics by holding a finger on the upper half of the watch screen.

Relativity StatsThe left column of numbers corresponds to the lower left dial (ie, energy+ or energy-). The right column of numbers corresponds to the lower right dial (steps, distance or AZM). While the statistics popup is being displayed, you can still change the mode of the energy and activity dials by long-touching them.

The upper three numbers show the following values:

  • Achiev: what you’ve actually achieved by the current time
  • Track: what Relativity thinks that you should have achieved by the current time
  • Goal: what you should aim to achieve by the end of today.

The lower three numbers show the following rates:

  • Achiev: the recent rate at which your achievement value has been increasing (energy and AZM rates are based on the increase in the last minute; step and distance rates are based on the increase in the last five seconds)
  • Track: the rate at which the ‘track’ line is increasing at the current time
  • Warp: achievement rate divided by track rate; ie, how many times faster you’re currently achieving compared to what would be expected.

To dismiss the statistics, hold a finger on the upper half of the watch screen again.

Settings

Relativity has several settings you can change. To find the settings, get into the 'Account' section of the Fitbit app on your phone, select your device (eg, ‘Versa 3’), and select 'Clock faces'. You should see Relativity shown. Touch it, and then select ‘Settings’.

Activity Period

This is the time period during which you’re expected to be active (ie, taking steps, travelling distance, acquiring AZM and burning energy above your BMR). See the graphs above.

Colours

You can change the colour of various sets of display elements independently.

Second Hands

You can show or hide the second hand for each type of dial (except for the date, which doesn’t have one).

Because AZM increases in large steps, the AZM dial’s second hand can appear to jump around randomly. For this reason, it’s hidden by default. However, if you prefer a consistent look, you can turn it on.

The energy and activity second hands can will sometimes jump at the start of a minute (explanation). The energy- dial can even drift backwards sometimes (explanation). While there are good reasons for these behaviours, if you find them too annoying, you may prefer to hide the corresponding second hands.

Extrapolation

Relativity only receives updated information about your energy and AZM achievements once every minute. This is obviously too infrequent to animate the corresponding second hands every second. To support smoother movement of the energy and AZM dials, Relativity can assume that the most recently observed rate of change will apply for the next minute (ie, until a new reading is available).

While this allows the hand positions to be updated every second, it also means that the hands can jump suddenly (including backwards!) at the start of a new minute, especially if you’ve increased or decreased your level of activity. This is because, while awaiting a new reading, Relativity extrapolates forward from the previous reading at the previously-observed rate. If the actual rate of activity during the current minute is significantly different, Relativity’s guesses will be inaccurate, and the correct reading will be applied as soon as it’s known (at the start of the next minute).

If you don’t like the sudden corrections to the dial times that extrapolation necessitates, you can turn off the extrapolation feature. Without extrapolation, the energy and AZM dials will only move once a minute, so you may want to hide the second hands for those dials.

Frequently Asked Questions

What does the +1 (or +2, etc) mean?

+1 on a dial means that you’ve met today’s goal, and are now taking steps (or calories, etc) out of tomorrow’s quota. For example, if your daily goal is 10,000 steps and you’ve taken 15,000 steps, the dial will show +1 and the time will be in the middle of your activity period (because that’s the time by which you should have taken 5000 steps tomorrow).

+2 means that you’ve already exceeded the activity goal for today and tomorrow (ie, you’ve done more than double the daily goal).

Because the default AZM goal of 22 is quite easy to obtain, you may find that the AZM dial can indicate many days in advance. If this annoys you, consider increasing your daily AZM goal in the Fitbit app.

Why do the times on the dials change suddenly?

By default, Relativity updates the times on the dials every second. This can result in sudden changes at the start of a new minute; see the explanation here.

If you turn off the extrapolation setting, the energy and AZM dials will only be updated once a minute because the watch doesn’t report changes to those values more often than that.

AZM poses a particular problem because, by default, you only need 22 of them in a day, and the watch only reports them as integers (ie, whole numbers). This means that the achievement one AZM will move the AZM dial ahead by about 30 minutes. Because of this, the second hand on the AZM dial is fairly meaningless when extrapolation is disabled, so you may want to leave it hidden.

Why is there a surge when I start to walk?

When you start walking, your watch doesn’t start reporting steps straight away. After a few seconds, when it’s more confident that you’re actually walking, it suddenly reports the steps it was ‘saving up’. So, when you start walking, your steps rate will be zero for a few seconds, but then it will suddenly spike as the backlog of steps is reported. The steps rate associated with that spike can be unrealistically high. However, after a few more seconds, that intial spike will drift into the past and your steps rate will settle down to a more accurate value. This phenomenon is most obvious when viewing the statistics popup.

Because the watch estimates distance from your step count, the distance dial and statistics can show a similar surge.

Why is AZM slow to start?

The rate at which you’re currently achieving AZM can’t be estimated until Relativity has been running for one complete minute. During this time, the rate is assumed to be zero. As a result, if you’re exercising hard when you start the clockface, you’ll see a sharp increase in rate after the first complete minute. This will appear as a sudden jump forward on the AZM dial.

This issue only occurs when Relativity is started; eg, after you close an app or swap from a different clockface. While Relativity is running, it keeps track of AZM increases even when the display is off.

How come the energy- dial is going backwards?

This is a side-effect of quantisation (discussed here).

If your BMR is 1.1 Calories per minute, your watch will usually report that you’re achieving 1 Calorie per minute when you’re inactive (because it only reports integers). However, 1 Calorie per minute is less than your BMR, so it seems like you’re burning less energy than the minimum possible. This means that you appear to be moving backwards compared to the ‘track’ line (see graphs above).

Even if you continue to be inactive, the watch will occasionally report a higher value (eg, 2 Calories per minute). This will move the energy- dial forwards by at least as much as it has recently drifted backwards. Therefore, in the long run, the energy- dial will not run backwards. The backwards movement is just a consequence of values being rounded down by the watch.

It would have been possible to suppress this effect, but it’s literally what the watch is reporting. It seemed better to accurately present the available information, even when approximations in that information lead to strange behaviour.

When the screen comes on, sometimes the statistics are displayed and sometimes they’re not. Why?

While the statistics popup is being displayed, Relativity has to do some extra processing to keep track of your recent steps and distance rates. When the screen goes off in this state, Relativity continues to record those values for a period of ten seconds, just in case you want to see the statistics again right away. However, after ten seconds, Relativity hides the statistics popup and stops recording those rates. This extends battery life.

Why does the statistics popup only display a few specific rates?

You must have a good eye for numbers to spot this!

The watch reports all achievements as integers, and it doesn’t update your achievements continually in some cases. Relativity estimates rates by calculating the difference between recent levels of achievement. Since those levels of achievement will always be integers, and some of them are small integers that don’t change very often, there can only be a few different rate values.

  • Energy. The watch only reports energy (Calories) at the start of every minute. Energy achievement usually only increases at about 1 Calorie per minute, although it can be ten times faster during exercise.
  • AZM. AZM is also reported at the start of every minute. AZM can only increase by 1 or 2 per minute.
  • Steps and Distance. Relativity estimates step and distance rates based on what’s been reported over the last five seconds. In that interval, the step and distance increases will usually be below 10.

Relativity owes its name to Einstein’s theory. Einstein also contributed to quantum mechanics, and this clockface’s limitation of only reporting a few specific rate values is a form of quantisation, so that’s another link to Einstein’s work. :)

Why doesn’t the statistics warp factor agree with rate at which the dial time changes?

The Track and Warp rates shown in the statistics popup are based on the expected accrual of energy or activity at the current time. In contrast, the corresponding dial will advance based on the expected accrual rate at the time it’s displaying. As a result, the warp factor can indicate a different value than the rate at which the time on the corresponding dial is advancing.

The difference is most obvious for an activity measure with no expected achievement outside of your activity period (such as steps). In this case, the statistics track rate will be zero. If you’re taking steps, your warp rate will be infinite. However, the time on the steps dial will advance at a rate based on the track rate during your activity period, since the dial can only ever indicate times during your activity period.

How can my warp rate be infinite?

For energy-, steps, distance and AZM, you’re not expected to record any achievement outside of your activity period (ie, the black ‘track’ line in the graphs above will be horizontal). However, if you do perform some activity outside of your activity period, your achievement rate will be a factor of infinity greater than the track rate of zero.