Pulse oxymeter use

On Thursday, October 3, 2019 at 9:45:05 PM UTC+13, John McLaughlin wrote:
I've searched this forum and google, but can't find the information - can
anyone tell me what readings I should expect to see at altitude?
Presumably, a steady decrease from the ground level reading, despite using

supplemental oxygen? But without a table of what's normal for each
altitude, how can you know when you need to be descending?

I believe the idea of supplemental oxygen is to keep within five points of your normal reading at sea level, and certainly no lower than 90.

I bought a unit a couple of weeks ago. I haven't used it in a glider yet, but today I spent 12 hours at 8000 ft pressure (presumably) in a B777. I dropped to 92-93 instead of my normal 96-97.