Run walk distance off by more than 10% between Series 2 and Series 3 watch

You have an interesting thought... I like the idea both devices could be off 5% creating a potentially larger gap. A stacking of tolerances per say... Thank you!

GPS is a pretty mature technology. Even the simplest devices have a pretty tight tolerance nowadays. I'm not looking for military precision. I have tested different devices in the past and the largest variance I have seen is less than 3%. I found it pretty disturbing to see such a variance on two devices made by the same company. I get that they are two different generations and the newer AW3 might be more accurate...

I do have an update... We again wiped everything out on both of our phones and both watches. I brought along another iphone that was not connected to my watch. I used the Runkeeper app on the phone that was not connected to my watch. This time, my watch (AW3) and the two phones I brought along were all within .08 miles of each other on a 3.65 mile walk. (2.2% variance) Additionally, my GF's watch (AW2) was off by .12 miles this time. (3.2% variance)

I cannot come up with an explanation why the results were so much better other than we did a complete wipe of the devices again and went through the calibration step at the exact same time doing the exact same path. We will continue to see if results remain this close or drift apart over time.