On Wed, 18 Jan 2006 14:33:17 +0100, davidof
wrote:

fat_boy wrote:
How? If a GPS devices prime role is to give the lat and long, it will
give you your position in terms of a flat grid on the earths surface.

For it to calculate speed, it measures the change in distance over time
relative to that flat grid.

So, unless the GPS unit ALSO measures altitude

they do

And devices such as the Garmin Geko 300 also contain an altimeter to
assist the accuracy problems with altitude detection. Also very
portable. I am not sure how it would stand up to the cold. The
batteries will certainly be rubbish in such temperatures.