Michael et al;
This is part of an email from a race director whose marathon course I measured,
"These garmin geeks are driving me crazy! What is your response? I am going
to post an explanation on the website and try to not use bad words."
I used some of your words in my response. This is the 3rd or 4th such question from a race director, not questioning the USATF measurement process or my accuracy, but looking for words that will make the doubt stop. Here's my response;
"USATF has considered using GPS for course certification and decided that it is less accurate than the approved (calibrated bicycle) method which is accurate to + or - about 3-inches of the reading on the counter mounted to the bike. The GPS unit is accurate to about 10-30-ft of the reading on the face of the instrument.
The 0.2 mile increased length noted by someone who doesn't trust the USATF certification process was due to the accuracy noted above and to not running the shortest possible distance, as the course was measured. Interference caused by buildings, trees and clouds also increases the GPS error while not affecting the calibrated bicycle measurement.
The USATF course certification program has been around about 35 years in its current form. It has been tested hundreds of times and found the best method to state with reasonable certainty that the course is at least the advertised distance. The credentials of the [your course] measurer; 25-years measuring, IAAF -B-Measurer, about 200 courses measured, 3 of those had world records set on them and were later length-validated by a separate measurement done by a USATF official. Hope this helps. I can dig up a much more detailed explanation of GPS accuracy, but it puts me to sleep and I'm pretty technical."
Pete Volkmar
Guido Brothers