Not yet investigated
What we have so far
A sigmoid, not a line. Above 90% saturation it is nearly flat and below it falls off a cliff, which is why the oximeter is precise where it does not matter.
This star is on the map because the show intends to take the question apart properly — the trials, how it is actually tested, whether the thing sold is the thing studied. That work is not done yet, and nothing here should be read as a conclusion. When the investigation is published it will appear on this page.