Originally Posted by
rumrunn6
someone told me that gps measures from point to point from space and so if you are climbing or descending it's not measuring speed accurately. gps for speed is only good it your riding on something level.
GPS is less accurate in vertical direction, but I wouldn't say "only good". Compared to what? If you use a traditional bike comp, 3mm difference in tyre diameter results to about 1% error in distance/speed calculation (700C wheel). Changes in tyre pressure can easily result in that kind of difference.
--J