Heart Rate Variability with the Bangle.js/Espruino

This is great! Which function seems to be getting called twice? I could take a look...

Would you be ok with adding this as an app in the Bangle.js apps repo?

Do you think the upscaling is really required? I guess I wonder whether it's actually giving you real accuracy or just the illusion of it.

If you're just trying to find when the peaks are I bet there's a way to estimate the time of a peak with subsample accuracy, for instance:

// looks pretty much middle of sample
*****
**********************************
*****

// you could be pretty sure this one was halfway
*****
**********************************
**********************************
*****

Also, if you really needed it I could add an option to raise the HRM poll rate.