Originally Posted by
wphamilton
If anyone is turned off by all the theory and math, it's pretty easy to compare precisions for yourself. Ride the same route a number of times and see how the GPS distance estimate varies, and compare that with how much the wheel sensor distance varies. Look at the measured track if it's available, and how much it varies from your actual path.
Here you go ... 10 rides on the same route, logged on a Garmin Edge 520 without a wheel sensor. The starting point probably varied by about 20 feet, and the finishing point by about 5 feet. If you dig into the files, you can extract a couple more digits for the distance, and compute some basic statistics:
Mean distance = 29.794 ± 0.017 mi. (Actually computed from 20 rides)
So, the relative uncertainty is at the 0.06% level.
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