In message , at 14:10:50 on Tue,
12 Feb 2008, John Rowland
remarked:
I've never really used a sat-nav system

Do they display a GPS speed?

TomTom does. It gives lat long as well.

It doesn't give height, though. Is it hard for GPS to be used to determine
height above sea level?

Height is much less accurate than position. It's also of little use to a
driver trying to find his way (rather than, say, a hiker on foot with a
map and contour lines, or an aircraft pilot).
--
Roland Perry