Originally Posted by F1_Fan
I've noted the same with my Polar 710i and Vetta 100A. I think the Polar works in 5m intervals, the Vetta, 1m. After a 2 or 3 hour ride the elevation gain on the Vetta is 50-75% more than the Polar.
Sounds to me like one of your altimeters is broken. I go on group rides with folks using a bunch of different brands of altimeters (Polar, Vetta, Specialized, Cateye, Avocet, etc.). There is never more than 20% difference between the highest and lowest cumulative elevation gains.