another example .... went for a casual ride with my mate today, and we cycled a route of 35 km. I used my Garmin Edge 1000 to record the ride, and my mate used his Iphone connected to Strava
The route was 35km long. I designed the route on RideWithGps
On RideWithGps, it states the elevation gain is 234 meters. On my Edge 1000, it recorded the elevation gain as 232 meters. (close enough)
On my mates Iphone using Strava, it recorded an elevation gain of only 182 meters.
Thats a huge difference on such a short ride. (50 meters). thats a 27% difference
when I designed the route, I dragged the little googleman on all the roads, and the google van had been on all of them.