I’ve found the blood oxygen feature on the Apple Watch to be worthless. The error bars on its measurements must be massive, so I would get numerous measurements every day down in the 80s. Better, finger-tip-based hardware measurements taken at the same time were never below 96%. And I’m careful about wearing the Watch just the way Apple recommends. I ended up just turning the feature off entirely, because I don’t want junk data in my Health history. I actually agree with Masimo’s CEO, who said, “I really feel wholeheartedly that consumers are better off without it."