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Good article. Thanks Pete. I was especially happy to see that he stressed people not running the SPR as the primary cause of the long readings, not inaccuracy of the GPS itself.

At one point it is mentioned that extra movement of the wrist may cause long measurements. I think if this is true at all, it has a very minor effect. Many people imagine the wrist as moving back and forth as you run, which it does relative to your center of mass. But relative to the ground it is always moving forward, just not at a constant rate. Any extra distance would come from vertical or sideways motion, and I think these are very small.
I will agree with Mark. As GPS units generally record their location only once every 100th of a mile (52 feet), or every second (don't know if you would have enough memory to record an entire marathon with this setting), the motion of the hand has nothing to do with the overall distance, especially since, as Mark said, the hand is always moving forward. The article said the side-to-side motion at a water station may make an impact, but I would argue it is not registered.

I also dispute that the overall distance for a marathon could be up to 84 meters long (don't they know how to spell over there???). The .1% SCPF should mean that the MOST a course may be is 42.1 meters long. It should be shorter than that, as the bike wobble will eat up some of the SCPF. There is no way to make it longer than 42.1 meters long, if calibration was done properly. I also take issue with the assertion that a steel tape is not accurate, since we take temperature into account, and put specific force on the tape.

But, overall, I think this is a very good article, which every runner who wears a GPS should read.

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