On Sun, 18 Nov 2007 00:00:00 +0000 (UTC), Bertie the Bunyip
wrote:

Hmmm, I've seen lightplane ones that have a GPS alt readoout. The other
would be handy for a loss of instrument situation, of course, but I never
use them in lightplane flying anyway..

I usually use the altimeter in the GPS in "barometer" mode, for
weather. It graphically plots the change in pressure for a constant
altitude over time.

The magnetic compass is useful when not moving, as GPS doesn't choose
direction well if there is no movement.