Originally Posted by DiabloScott

One fellow I follow recently rode 14 laps around his neighborhood in the late afternoon. His elevation chart looked like he was going downhill the entire time - he posts here and is public so check this out: http://www.strava.com/activities/93277888

He uses a Garmin Edge 500 that has the altimeter function. The GPS elevation data will more likely be consistent from ride to ride even if it does sometimes give funny results when riding over a bridge.