When I originally got it I tested it on a known hill (Old La Honda) and it reported the exact altitude I saw in some descriptions of that climb.
The Vetta also has a % grade measurement, and it works while you ride. It is also as accurate as the reported grades.

I like the Altitude function of the Vetta, but I do not like the speed/cadence and the way the wireless was implemented. The speed or cadence update on the display every second (or longer if you ride slow), Also, if you stop somewhere for more then a few (4? 5?) minutes it goes to sleep and you need to press a button to wake it up..