after spending some time in neuro post-op several years ago, I was intrigued with a disposable blood oxygen sensor with a red LED that clamped to my fingertip.  it obviously put out a voltage and this machine interpreted it.  that's my vote for useful info on a x/c trip across Colorado at 15,000'.  mt mtn air unit shows oxygen flow rate, but my blood level is what truly matters.  I'd guess that the flow rates are also double or triple what they need be, since humans are so different.  this could be a great stand-alone instrument as well.        kevin