fat_boy wrote:
: I have heard tell of using GPS, but since it will only get your
: horizontal speed component, and not the verticla, it will always read
: low.

Last time this came up someone did the maths and came to the conclusion
that ski slopes are nowhere near steep enough to make a major impact on the
speed - even if only the horizontal speed is measured (despite what skiers
might like to think!). As others have pointed out GPS receivers account
for height anyway - some (the barometric sensor types) better than others!