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Accuracy Guarantee


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Guarantee? Somewhere on the face of the same planet.


As to what the expected accuracy is, it's largely a function of the individual unit, the technology it uses, and which features are being used at the time. My old eMap is a 12-channel unit, and wil exhibit more accuracy than older models, but it hasn't got the WAAS augmentation, the computational horsepower, or the apparent higher sensitivity of modern units. The positions of the satellites in their orbits, relative to both the receiving unit and each other, can also effect the positional accuracy.


If you're looking for a number, I usually find that my eMap will get me to anywhere between 10 to 50 feet of the cache under most conditions. I've had a few hunts where it put me right on top of it, and some where I had to poke around for half an hour to find it. Without having a "known good" set of coordinates to base accuracy on, this is all relative not only to my own unit, but that of the hider's as well.


I've long thought that I should find a few recently-verified benchmarks to judge the actual accuracy of the eMap, but it's always gotten me into pretty close proximity to the caches, so I've never really felt the need to find out for certain.


Truth be told, for my purposes, "close enough" is "good enough".

Edited by Seamus
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Guess I don't expect any guarantee, but I do have expectations. They, of coarse vary with conditions (tree cover, the like). With good signal and no threat of multipathing, I expect 6'-20' feet with 10'-15' most common. With WAAS under good conditions, 3'-10'. Under less then great conditions, 30'-80' is not uncommon.

This all is based simply on personal experience, and not technical claims.


How'd I do?

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I expect it to take me to the end of the runway or to the offshore rig when the visibility is down to a mile or less. My life, and the lives of my passengers, depend on it. It does that, every time.


The exact accuracy depends on lots of things, including the GPSr, the antenna, the conditions, where the satellites are and how many are in view, ionospheric conditions, and lots of other things. 30 ft is about the best you can expect under most conditions. Given a poor GPS under wet trees, and 50 ft isn't unreasonable.

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I find that different brands of GPSrs also play into the accuracy factor. For instance, I marked a benchmark in the local area where I hike all of the time with my old eTrex yellow. When I go back and try to find the benchmark with the eTrex, it would usually fall within 5 feet or so of the mark every single time. Then, once I tried finding the same mark with my iFinder, it was about 15-20 feet off. To verify that it wasn't the iFinder's inaccuracy, I placed a waypoint with it and then navigated to it several times with an accuracy of no more than 5-8 feet.


This means that there might be very slight variations in each brand of GPS out there.

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