A person who writes software for GPS devices told me yesterday that their ability to give you a sensible height is basically crap and that this is inherent in the technology.
(IFR approved GPS devices might do very much better than others, he was maybe not talking about them.)
Here's an example statement from a GPS manual:
"WARNING: The KLN 94 displays GPS-derived altitude on the AUX 1
page. Due to many factors, GPS altitude may typically be several
hundred feet in error. Do not use the GPS-derived altitude for navigation."
Last edited by Gertrude the Wombat; 3rd May 2004 at 15:37.