# Placing first Cache. Best way to average coords?

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Goona do it. Gonna break. Been looking. Been searching.

Time to place my own.

Got lots of ideas. Micro-cache. Theme cache.

Is it to just take a straight average of a bunch of readings? Do I just add and divide by the number or is there somne special way to average coords?

Thanks for the help.

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A lot of GPS units have an average function. On my Garmin V, it is buried in a waypoint menu. Check your manual.

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quote:
Originally posted by Echo2000:

When I placed my first 2 caches I went to the spots three times and took 3-4 waypoints each time. I walked at least 100 feet away then walked back and let the GPSr settle. After that I just did the math.

When I placed the caches I re-checked the coords one last time.

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As always, the above statements are just MHO.

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What I do is reset my GPS and take a reading. Then I walk about 100ft away and reset my GPS again and walk to the cache. If I am within 3-6 feet, I verify it again. If that works, then I call it good. If not I start over.

Dan

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Averaging coords using the GPS averaging function over a short period, like 20 minutes, will not necessarily give you better accuracy. The GPSR will average all values it gets during the 20 minutes, including some bad ones. Probably the best way to average is to take coords only when the GPSR indicates a low EPE (error value) and to take positions at several times separated by at least 30 minutes. You can average these positions graphically using the map page, or numerically by simply averaging the lat/lon values. If the cache position is in heavy cover, it may be better to take coords from an offset position which is more open, and then project back to the cache position.

If you average coords taken at intervals of at least 30 minutes, the accuracy will improve by roughly 1 divided by the square root of the sample size, e.g. if you take four positions with an accuracy of 18 feet, the averaged accuracy will be about 9 feet. For 9 averaged positions, accuracy would be about 6 feet.

FWIW,

CharlieP

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