"kage" wrote in message ...
Thomas,

Well it might be wrong, but it will be close, like I said----not exact. And
it is a good preflight check to see if there are gross errors in the
instruments.

True, but atmospheric pressure isn't involved in this test at all. You
are comparing altimeter setting with altimeter reading. You are just
verifying the altimeter setting. Pressure really has nothing to do
with it. They should never have labeled the altimeter with numbers
like 29.92. They should have just called them 123, etc.

If the actual pressure did change, it would change both your altimeter
reading and altimeter setting, so pressure isn't really relevant to
testing your altimeter against the altimeter setting.

-Robert