No one has mentioned using the manifold pressure guage as an altimeter.
Because you can't do it in the air, unless you stop the engine first.

Well, you can, sort of, but it probably won't help much. At full
throttle, the manifold pressure will max out at a value that has the
same relationship to altitude as an altimeter. I vaguely recall it's
something like an inch loss per thousand feet high.

Jose
--
"Never trust anything that can think for itself, if you can't see where
it keeps its brain." (chapter 10 of book 3 - Harry Potter).
for Email, make the obvious change in the address.