"Stefan" wrote in message
...
mike regish schrieb:
The point is that the pressure altimeter measures, well, a pressure, not
an altitude. It displays a value in feet, but actually, this is wrong.

Certainly true.

... the whole aviatic system (airspace boundaries, ATC clearances, traffic
separation) is based on pressure altitude

I agree with that statement too.

.. If you are given an ATC clearance for a certain pressure altitude but
fly GPS altitude instead, then you act exactly like that bozo who drives
on the wrong side of the road.

The only ATC clearances for a pressure altitude would be in the flight
levels. Since the question was about setting a pressure altimeter, I would
say that the flight levels are irrelevant. Below the flight levels, ATC
clearances are for pressure compensated altitude above MSL, so yes it is
based on pressure and not true altitude but close enough. My GPS gives me a
calculated altitude above a theoretical sea level that's also close enough.

-------------------------------
Travis
Lake N3094P
PWK