Altitude Compensation

[Robert J. Harris]

>From what I read and hear, the Air Flow sensor used in production
EFI's at best compensate for temp and density changes in the 
intake air mass.   Then the oxygen sensor is used to fine tune
the mixture to a rich power setting - I.E. no uncombined oxygen

Does anyone do any altitude compensation?  Because, as altitude
increases, not only does the air mass density decrease, but the
percentage of oxygen decreases (simple physics - check books
before questioning or flaming) and the oxygen decrease is independent
of the density decrease.  

Basically, this means that to maintain a constant fuel /oxygen mixture
(which is what counts because the rest of the air is meaningless for 
combustion) for a given power, more air most be ingested and a leaner
fuel/air
mixture used or it becomes overrich.  Incidentally, why you lean out
a piston aircraft engine at altitude is more to avoid a cool burning
 overrich mixture slowing carboning up and fouling out your engine than
just enhancing economy.  

Basically, as I understand it, the oxygen sensor corrects this after the
fact.
Is there any sensors that compensate the air flow value for the altitude 
related decrease in oxygen?   Note that this is not a problem on excess
oxygen engines such as diesels and gas turbines and why they do not
loss power in the mountains like gasoline engines do.

Remember the Reichstag

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