Apple Watch overestimate Blood oxygen level during sleep

There is an inherent flaw by which Apple Watch measures blood oxygen during night sleep. I noticed that every night I get at max 5 readings during sleep, which is way too less to assess anything. The algorithm is designed to take readings every 30 min. One of the reason is that Apple watch needs to be so, so still during blood oxygen measurement that slightest moment refuse the reading. Its a assumption that you need to be absolute still for apple watch to work. Its a faulty assumption, imagine if your blood oxygen drops to say 87% due to sleep apnea or obstructions, the normal response of your body is to move and be restless to get more oxygen. Well, Apple watch will not measure then. That is why your reading always looks good coz Apple watch only measure when you body is at peace and has good oxygen levels. Its false positive! Another wierd thing is that, if you are not still at designated 30 min reading time, Apple Watch skip that half an hour altogether, instead of reading say after 3 or 5 min. Hence, if you sleep for 8 hours and just move slightest after 30 min, your Apple watch will not record any blood oxygen. The the level of programming of a trillion dollar company!