OT Don't read this (was Re: Altair MBL source)

[der Mouse]

> Note that the body works perfectly well with substantially less air
> than you get at sea level -- that's how you function in an airplane.

"Less air" for what value of "air"?  What the body wants, as I
understand it, is a partial pressure of oxygen at least vaguely equal
to that in the air it's used to.  On airplanes, this is done by using a
gas mixture (proportionately) richer in oxygen than air, at a lower
pressure.  (There are other issues associated with this too; for
example, you don't want to lower the pressure too fast or you risk
giving your passengers the bends.  And anyone who hasn't learned to
equalize pressure by opening the eustachian tubes between the
nose-mouth cavity and the ears is liable to have uncomfortable ears.)

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