Apple Watch 6 blood oxygen measurement said I had hypoxia when I in reality was fine. How to know if reading is taken in optimal conditions? TL;DR: How can I know if the SpO2 reading is in fact taken in optimal conditions ?

I wanted a new watch for exercise tracking, so I looked at Apple Watch 6. I was also excited about this SpO2 feature that the Apple Watch 6 has, even if I really don't need it. This feature is the main new feature that they are marketing their watch with. Just check out their web page and it is basically the headline for the watch. Also, in these covid themes, this is suiting, right ? So I bought the watch, and I know that this is not for &quot;medical use&quot;. I am 35 years old and fit, I am very healthy and I exercise almost every day, and there is nothing wrong with me as I know. I tried the feature, and it always read between 87 - 91, suggesting that I might be hypoxic. Or in these times, considering my good health, that I might have COVID-19. I knew that this is probably not accurate, but what if the watch is right ? I developed a concern over a few hours, and I went out late at night to a pharmacy and bought a 100 euro medical grade pulse oximeter (SpO2). In that way, I could know for sure if I had to see a doctor to check if I have an unknown heart or lung issue, and yes, I could sleep at night if the oximeter says so! And guess what! My SpO2 is at 99%, steadily. Perfect! I kept taking readings with the SpO2 meter on my finger at the same time as with the watch, and the watch said that I had hypoxia almost all the time, while the SpO2 meter said I had 99% SpO2. I tried different tightnesses of the strap (tight, loose, in between), and I put the watch at different positions on my wrists, and further up on my forearm to get a larger contact surface, all kinds of things I tried. My pulse was between 60 - 90 bpm, and I was in room temperature, and had normal body temperature. However, sometimes the watch said I had 100%. And the next reading showed for example 90%.
So, basically, this gave me a lot of unnecessary concern. Apple customer service said that &quot;well, it is not intended for medical use, so there is nothing we can do&quot;. I went through (spent 3 hours) everything with customer service, the HW diagnostics and the watch is perfectly fine, and there is nothing more they can do. They claim that erroneous reading might be because you are moving your arm or something like that a little bit. But how can you know ? Am I supposed to assume that low readings are because of the watch not touching the skin in the exact right way in optimal conditions ? How can I know if the reading is in fact taken in optimal conditions ?
What if someone is sick with COVID-19 and have hypoxia without knowing it, and the watch shows 100% ? Maybe that will make them delay their visit to the doctor and get worse ? Of course they might be aware that it is not a &quot;medical device&quot;, but still, it can affect their perception and decision. And what is the point having such a feature if it doesn't work ?
In my case, I wasted 100 euros, hours of my time, and as I see it now, money on a watch. I want to return it because of this, but I can't because I bought it in a third party store. Apple basically says that it is my problem. It is not intended for medical use, and if someone has a concern, they should see a doctor. Well, it did indeed gave me concern, and for nothing. If it was not for the watch, I would not waste money on an oximeter or consulting a doctor - for nothing! What is the point with that ? I am sitting there with a watch with a main feature that doesn't work, and that tries to give me anxiety, and it is my problem.
But - worse, is that people might get erroneous assurances for their SpO2 levels. That could be in the worst case fatal in the time of COVID-19.
As much as I understand your frustration, Apple mentions the limits in the small print at the bottom of https://www.apple.com/watch/:

Blood Oxygen app measurements are not intended for medical use, including self-diagnosis or consultation with a doctor, and are only designed for general fitness and wellness purposes.