GPS as a measuring device

rickmelansonMember

I am sure some of you have come across this question before. I do the timing and race results on most of the courses I measure for Certification and on a new 5K and 20K ran this past week-end I had a couple of people come and comment that the 5K was actually 3.2 miles and the 20K was 12.6 miles. And the reason they know this is because they ran with a GPS strapped to their arm. My initial inclination was to tell them to not trust the fancy instrument but I am sure that someone who spent a couple of hundred dollars on the device would not like to hear that. Is there a good response to people who, I'm sure, will start asking this a little more often as time goes on. I want to have an answer that sounds like I know what I am talking about, rather than taking offense to their suggestion that my course is actually too long. Would appreciate any comments.

10/25/045:38 PM

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jimgerweckMember

Rick, it's that Southern gentleman in you that keeps you from doing what we'd do here up North - tell them to get a life.

Seriously, I've been doing some testing of the Garmin Forerunner for Running Times, and I find it's fairly accurate, but not totally so.

First, it gets thrown off by trees, wires, tall buildings, which cause it to lose a good signal from the GPS satellites. And even when it doesn't the manufacturer only states it is 99 per cent accurate. I ran a certified 3.05 mile course by the beach, and it came up with 3.10,

You could tell the people 2 things: 1. The system is only 99 per cent accurate, and less so if there's interference.
2. They probably are not running the SPR.

These 2 factors would combine to produce the "overage" you describe.

10/25/046:08 PM

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