The channels a stretch recorded. A channel the activity didn't record is null, and so is every one when its samples have no timestamps.
null
Metres from the start, on the activity's distance axis (a pool swim's lengths, else GPS or the device's distance).
Worked out from distance and time between samples, not recorded.
The channels a stretch recorded. A channel the activity didn't record is
null, and so is every one when its samples have no timestamps.