Why GPS Watches Always Measure Race Distances Longer

In this past year I’ve had a Garmin GPS watch, I’ve run about a dozen races while wearing it.  In every race, without fail, it’s always the same: the end distance on the watch is always longer than the race distance.  The Broad Street Run 10 Miler may end up as 10.12 miles, and a marathon may show up as 26.44 miles.  The additional one or two tenths of a mile may not seem like much, but they matter when you’re trying for a particular time goal or if you’re saving your energy for what you believe is the final distance only to find out that the race is not over.  And, of course, the GPS watch never measures the distance as less than the race distance.

Is it the watch, the course or something else?  After being stumped, it turns out that the answer is it’s the way the course is measured combined with slightly less than completely efficient running.

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