ReadonlychannelReadonlyunitThe unit values() and toTimeSeries() hold: 'bpm', 'W', 'rpm',
'm/s' or 'm'.
The sample at index (negative counts from the end).
Each sample's instant, in milliseconds since the epoch (a copy).
Seconds from the activity's start, one per sample (a copy).
As a pond TimeSeries with one value column (in unit), keyed
by each sample's instant. A gap is a missing cell. Shares the
activity's own storage: nothing is copied.
The values in unit, one per sample, NaN in a gap (a copy).
One channel's samples, in order.