So I just came across this and I have the same situation on my 7. I do have mild apnea and I compare my data from my watch with another 02 device and it is drastically wrong some nights.
Last night is a good example. My range on the other device is 90 to 99. My watch says 80 to 94 and 80 to 97, broken into two parts for sleep because I got up to use the restroom.
The worst part is that the graph itself is a mess. It's almost condensed to where it actually looks like my ranges are 80-91, and 80 to 93. None of the top marks look like I was anywhere near 97% all night and half of the night looks like I stayed in an 80 to 88 range for hours... which isn't possible or I'd feel absolutely terrible right now.
I get that the watch is not meant to replace or be as accurate as a medical grade devices but that seems a bit of a cop out to me as you clearly mentioned in your post that you compared yours with other watches from other companies and it was still way off. Those aren't medical grade devices either so you're not comparing apples and oranges, you're comparing oranges to oranges and it's still coming out horribly off.
Even when my numbers are somewhat accurate, the graph itself doesn't match what the watch is reporting as explained above. See photos. Look how far from the top of the graph the lines are...
Someone mentioned on reddit that they think the graph is not properly calibrated with the sensors. Either way, even their own graph disagrees with their own data. It really makes little to no sense. It's not even a reliable "basic guideline", which is just embarrassing for the money people pay and compared with other smart watches. It isn't even a new problem. It's been like this since I had my watch 4. Honestly they should give up the graph altogether if its not calibrated properly and just provide a 3 min intervals graph like they do with heart rate. It would be better than nothing.
