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Which Gps To Believe

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I just got a Magellan SporTrak and took it out caching for the first time today. I took it to a cache I had found last year, and a good thing too, because the co-ords were over 130 feet off, in the woods that's a lot of possibities. I was a little miffed because my little yellow e-trex was always pretty good, and it got me much closer to the cache site a year ago. When I got home, I started to compare the two, taking waypoints around the yard, and then following up with the other unit. Never got back to the same spot twice. Maybe bad sat day? Started looking at them side by side, always different. Took them both on another cache. Both correctly got me to the cache site, but when I was closing in on the cache, ETrex said 20' east, Magellan said 30' north. and my son was busy finding the cache 20' west. My question is this - Do the rest of you with multiple GPS's notice that they read different? How much? By brand/model? Does it drive you batty? It's like having two watches, your never really sure of the time!

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As the old quote goes. " A man with a GPSr knows exactly where he is. A man with 2 GPSrs will never be sure" :lol:


My (then) BF and I both got Megellan Sportrack Maps. They were never the same. I'd say 10 feet, his would be 25. This is why the game is a bit harder than most muggles figure. Check the specs for your GPS. It probably says something along the lines of "accurate to with in 9 meters".. or roughly 27 feet. Use which ever one you like best. You'll still find em.

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Yup, I use a SporTrak Pro, and my son uses an ETrex yellow. Once we get to ground zero, rarely do they agree. Neither seems to have the edge over the other for actually locating caches. I typically find them more often than my son, and though I'd like to chalk that up to Magellan's superiority :lol: (along with WAAS), I have to grudgingly admit that it's more likely my "geosense" rather than anything else. After all, he's only 11 and hasn't been using the ETrex as long, though some have stumped me that he practically walked right up to.


Lets look at the accuracy reading for a sec. That is only an estimate by the unit itself of it's own accuracy. That alone makes the number suspect, as far as I'm concerned. In addition to being based on the conditions (i.e. satelite numbers, strengths, positions, etc.), it's also based on the individual unit's software programming and how "optimistic" that programming really is. That's like a boxer telling you that he's the greatest. I don't believe for a second that all manufacturers use the exact same criteria to come up with those numbers.


Rather, if I'm getting high EPE numbers, then I assume that it's having trouble getting good signal. If I see low EPE numbers, I assume it's getting a pretty good signal. But I ignore the actual number given, because I don't believe it. In other words, if your unit says it's getting 10' accuracy, and you restrict your cache search to only within a 10' radius, you're going to have alot of DNFs.


Next, while in theory, a pair of GPSr's will lead you to the same place on the ground as long as you are using the same datum, you also have to allow for that error. If we actually believe the unit's accuracy numbers (which I don't), and if both units are reading an accuracy of 25', then both could be giving the exact same coordinates even though they are 50' apart, and both would still be right.


In the end, I have to agree with that quote: "A man with a GPSr knows exactly where he is. A man with 2 GPSrs will never be sure".

Edited by 4x4van
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