getHeartRateHistory () doubt, iterator data.

Actually neither.  It varies by device and is based on screen with so a 4hr graph can be displayed by a native widget.  Each sample has a "when" and by comparing two adjacent samples you can see the frequency of the readings.  It's been a while since I've done that, but on one devices I remember it was 94 seconds.

The number of samples also varies between devices, though in the sim it's a fixed number.

OK I understand. Thank you very much for the explication.