HRV - Heart Rate Variability

That's great - thanks for posting it up!

Do you know what the sample rate is for that raw data array?

I just checked, and it's 50Hz.

Just a note about this though - Espruino includes the raw data array that HRM values are reported into, and they actually continue to be added to the same array - so if you're a little slow processing the array you'll find that the values at the beginning start to change!

If you're doing a lot of processing it could be worth copying the HRM data to a new array first:

var hrmData = new Int8Array();

Bangle.on('HRM', function(hrm) {
  hrmData.set(hrm.raw);
  // now work with hrmData
);