On Thursday, October 3, 2019 at 9:45:05 AM UTC+1, 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?

Here is an article which appeared some time ago in the Soaring Magazine

https://1drv.ms/b/s!AgdlgPN7f_vjtxeDhiWV1ohboBQ9