This is really great! Thank you.
I developed a breathing app (https://www.lungy.app) last year - we're actually doing a study at the moment looking at how heart rate variability changes with breathing exercises. We're using a polysomnograph for gathering the data at the moment - using a Polar H10 may be much simpler. Is it possible to get the raw ECG lead data, or is it just BPM at each time step?