Jose wrote:
I'm 69 yrs old and have the Nonin testing unit. I've had the Arrow up
to 13,000 and find that I can maintain O2 at 90+ with regular slow,
deep breathing.

That's without supplemental O2?


Yes, without supplemental. I know that 90% isn't great, but this was a
test case on a beautiful clear day to check out both myself and the
Nonin. Normally, over 10K I use the tank for at least part of the
flight.