I found that a pulse ox meter was little help in gauging my true condition in oncoming crisis. The only thing that really seems to be a real home gauge is how far you can count aloud on your deepest breath. If you are like me, a talkative singer, lung capacities will also differ. In my own case, by the time I was only able to count to 15, quickly, only the upper quarters of my lungs were functioning. I have heard 12 is the real "worry point" from a doctor's view (ie emergency action necessary). Yesterday I could count to 24, but was finding the cpap to be a relief and was flattened otherwise. On a "good" day, I can count to 50. Through all of this, the good ol' home pulse ox will show maybe 96%. Take that as you will, but BE careful.