How about doing a touch and go at an airport with a known altitude,
while you are retracting flaps, quick twist of the dial to set field
elevation and away you go.

(this was a joke by the way, much as the original question)

Neil Gould wrote:
Recently, Mxsmanic posted:


"Jim Macklin" writes:


GPS, even a $100 hikers model will solve the problem. But I
just say, look at the ground, you can judge 1,000 feet
pretty well and you only need to apply the hemisphere rule
above 3,000 AGL.

GPS is far less accurate than an altimeter, and I don't think the
regulations say "if you have no radio, use GPS."


I'm not sure why you think that "GPS is far less accurate than an
altimiter...", as an altimeter only need be accurate to 75' to be legal.
GPS can do much better than that, and are unaffected by barometric
pressure; the result is a potential source of problems that require pilots
to fly by the altimeter, not the GPS. None of this has anything to do
with regulations, of course.

To answer your original question, the prudent pilot will take the
barometric pressure of their destination into consideration during
preflight planning, and adjust the altimeter accordingly. Most of the
time, the pressure won't change all that drastically at the destination in
the time it takes to fly 100 miles, and non-radio VFR pilots aren't likely
to fly in weather where the pressure is changing too rapidly.

Neil