[mint5]

It may depend on skin type, body composition and wrist hair - perhaps the validation work used a skewed sample?

I’ve found the sensor to give stable results, with repeated measurements always within 2 percentage points.

And the results give qualitatively very reasonable data when I sleep at high altitude. The readings have a clear dependence on the elevation.

I haven’t cross checked against other meters, but my Apple Watch 9 sensor gives stable and reasonable results that match expected altitude trends. So yeah it may not be tuned to a wide enough variety of wrist types.