I never understood how two systems (Strava and Garmin) that interpret the same GPS data points, can be so different in their calculations sometimes.

Totally weird.

Different base maps perhaps? I used to map out routes on RA and Mapmyrun. There was a huge difference in the numbers. Afterwards, Garmin would give me a different number - usually somewhere in between. I figured the difference was the sensitivity of the base maps. 10' contours vs. 10 m. contours for example.

Good point. In either case the junk in my trunk is feeling it. lol

 

I never understood how two systems (Strava and Garmin) that interpret the same GPS data points, can be so different in their calculations sometimes.

I'm pretty sure Strava does corrections to roads/known paths, Garmin reports elevation where it thinks you are which may or may not be accurate (ex. there's a small ridge right next my house - Garmin often thinks I start/end my run up there instead of on the street, difference of ~10ft of elevation, if that happens a few times over the course of a run it'll throw the total elevation gain off a fair bit).

 

Excellent point also: if Garmin uses the elevation of where it recorded the GPS point, and Strava goes "that is probably an error, I bet you were actually here", then that would make a difference.

 

My watch has a barometric altimeter, and I know Garmin uses that when it's available (their own product, after all). I don't know what Strava does in that case. Since I don't run much elevation, it's not something I keep track of.

Mine does not, so it's even less accurate. Having said that being in the ballpark was good enough for me, which is why I chose the 245 over the 645. The 645 has a barometric thingy built in, but cost 100 dollars more.