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Re: [RC] [AERCMembersForum] GPS - "As you know..." - Don HustonTHE DOCUMENTATION IS WRONG. Some GPS units including the Garmin GPSMap 76 series and 60 series are within 2-5% when satellite reception is not broken up. I am a surveyor. I use a handheld Garmin GPSMap76S to find lost survey markers. Here are some tests of accuracy that I have done. First: the "location" test and I have done this many times before. Monday I calculated the GPS coordinates for a survey done on some property 60 miles from my office. At the jobsite the property owner pointed out a corner he had found and the coords on my GPS unit were only 1 meter (3 ft) off from the calculated true position (had maximum satellite reception). Therefore this GPSMap76S can in fact "locate" where you are very accurately. Second: the "distance" test. I have software (nRoute by Garmin) that will follow roads and highways from one address to another and give me the mileage. The software said 486 miles from my boarding stable to the basecamp at Hurricane. I drove the exact route, the GPS never lost signal and got 490 miles. The extra was probably from stopping for gas etc. I have GPS'd Sunland 50, Fireworks 50, Warner Springs 50, Eastern Mojave 50, Bar-H-Boogie 50, Git-R-Done 100 just to name a few that used trails that show up on my Topo! software and OzieExplorer software using GIS digital photos. On those rides my GPS got the same mileage (within 2-5%) of the mileage generated by following the visible trails on the software with the mouse. Therefore this GPSMap76S does in fact measure the "distance" along a highway or a trail very accurately. So...if the locations are accurate and the distance between locations is accurate (2-5%) then the overall accuracy is 2-5% for this GPSMap76S. The key to accuracy of course is reception and how the GPS is set to record the trackpoints. I use a CamelPak that has a pocket top and center to hold my GPS. That way nothing blocks the reception except heavy trees or deep canyons and when that happens I can use my software (if the trails are visible) to fill in the blanks to get a very accurate (2-5% short) trail mileage. I set my GPS to record trackpoints based on distance (0.01mi = 53ft). The great thing about a distance setting is whenever I stop for water or a vet check it shows up on the software as a large block of time with no distance and no wasted trackpoints. So I never have to touch the GPS during a race and I still get a record of time and location for every stop.At 11:53 AM 3/21/2007 Wednesday, Susan wrote: It's documented. GPS measures short by 10 to 20%. It's been discussed on this Forum, Ridecamp, the Racewalking Forum and I've seen crossposts from other lists as well. *I* didn't make this stuff up; I've read it and experienced it, however. Congratulations on your good fortune. SanDiego, Calif
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