"Peter Duniho" writes:

The FARs require the use of oxygen. They don't stipulate how much to use.
So, you can either rely on the calibration of your oxygen equipment, or you
can get some actual feedback on whether you are getting enough oxygen.

Indeed. Once on the way home (Indiana) from California I stopped in Colorado
and needed oxygen. They didn't have the required fitting so I flew home with
what I had knowing I could always go lower if I ran out though it would
probably mean an extra stop for fuel. (I was VFR and it was VMC all the way
home. We have a big O2 tank and only two people.)

I reduced my wife's oxygen flow (because she was just resting anyway) but
when we crossed the Mississippi and she couldn't think of the word "barge" I
stuck her finger in the oximeter. She wasn't terribly low but she was lower
than usual so we increased her flow a bit.

And before I got the oximiter there was the time that I almost passed out
because I didn't notice my cannula had slipped while I was relieving myself
over the Rockies...

--kyler