So the Apple Watch is in an accurate heart rate monitor? Or is high precision not needed for testing for this abnormality? I want highly accurate rate monitoring throughout the day, especially on long hikes.
Also, when I first tried it I had wrist pain, and learned that I actually was "wearing it wrong". Moving it further up my arm fixed it, and now it's literally my favourite device.
So my guess is it will be the same: just as good as my Polar chest strap when snug, and off when, well, off.