Clocks

A recording holds several kinds of time, and mixing them up gives wrong answers: an average pace on the wrong clock, a training load that counts a café stop. fit keeps them apart.

Clock	Meaning
elapsed	Wall-clock time from the start to the end
timer	Time the device's timer was running, as the file states it
moving	Time judged to be moving
swimming	A swim's time spent swimming, rests at the wall left out
rest	A swim's time not swimming (elapsed − swimming)

The ride shows the first three apart. It stopped at a traffic light for 45 seconds with the timer running, then paused the timer for six minutes at a café:

import { readFileSync } from 'node:fs';
import { readActivity } from '@pond-ts/fit/files';

const ride = readActivity(readFileSync('hill-ride.fit'));
const { time } = ride.stats();
console.log('elapsed', time.elapsed?.format());
console.log('timer  ', time.timer?.format());
console.log('moving ', time.moving?.format());

elapsed 1:39:54
timer   1:33:54
moving  1:33:11

Elapsed counts everything. The timer leaves out the café, because the rider stopped it. Moving time leaves out the café and the traffic light, because neither was moving.

Picking a clock

stats() works on elapsed time unless you pass another. The answer says which it used, in basis, and pace, speed and the channel averages follow it:

for (const time of ['elapsed', 'timer', 'moving'] as const) {
  const s = ride.stats({ time });
  console.log(
    s.basis.padEnd(8),
    s.speed.average?.format('metric'),
    s.heartRate.average?.format(),
  );
}

elapsed  27.0 km/h 133 bpm
timer    28.7 km/h 133 bpm
moving   29.0 km/h 133 bpm

On the timer basis the channel averages are the same as on elapsed: a device writes samples only while its timer runs. On the moving basis they are taken over the moving samples only.

How moving is decided

Moving is decided by sport, because "stopped" means different things:

• Runs, rides, walks, hikes and open water swims: the time between two samples is moving when the speed over it is at least 0.5 m/s (1.8 km/h). A bike coasting downhill is moving; a runner standing at a crossing is not.
• Pool swims: only the time spent swimming a length is moving. The rests at the wall are the stopped time. See Pool swims.

The Moving time guide builds the speed rule from scratch.

A clock that isn't known is null

When a file doesn't record its timer, the timer time is null, and so is everything worked out on it. It is never filled in with the elapsed time. An activity built from bare streams has no timer:

import { Activity } from '@pond-ts/fit';

const seconds = Array.from({ length: 601 }, (_, i) => i);
const noTimer = Activity.from({
  activity: {
    id: 'manual:1',
    source: 'manual',
    externalId: '1',
    name: 'Ten minutes',
    startTimeUtc: '2026-06-20T07:00:00Z',
    distanceMeters: 0,
    movingTimeSeconds: 0,
    elapsedTimeSeconds: 0,
    elevationGainMeters: 0,
    sportType: 'Run',
  },
  streams: {
    latlng: [],
    timeSeconds: seconds,
    distanceMeters: seconds.map((s) => s * 3),
  },
});
const onTimer = noTimer.stats({ time: 'timer' });
console.log(
  onTimer.time.timer,
  onTimer.pace.average,
  onTimer.time.elapsed?.format(),
);

null null 10:00

Swimming and rest

A swim has two more: the time spent swimming, and the rest between. Any other sport has neither, so both are null there.

const swim = readActivity(readFileSync('pool-swim.fit'));
const sw = swim.stats();
console.log('elapsed ', sw.time.elapsed?.format());
console.log('swimming', sw.time.swimming?.format());
console.log('rest    ', sw.time.rest?.format());
console.log(
  'pace    ',
  sw.pace.average?.format(),
  '→',
  swim.stats({ time: 'swimming' }).pace.average?.format(),
);

elapsed  27:01
swimming 23:21
rest     3:40
pace     20:47/km → 17:58/km