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Y2KOTA

How can I check the accuracy of a used GPSr I just bought?

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I went back to a cache that I could find by using other means that I have founds with. Such as the maps on the "View Cache Details" pages, other clues and common sense :wub: The GPSr sent me about 300ft to the west. I ended up in the middle of the street of the neighborhood next to the park that the cache is in :D I also went to anther cache I did find. The cell phone I just bought with the Geocache Navigator™ installed was reading right on the money. While the GPSr coordinates are constantly off by latitude minutes of 00.020 and longitude minutes of 00.080.

 

I would love to be able to find a way to check so I can have full confidence in the unit. Any help here would be very appreciated :wub:

 

If it maters its a Garmin GPS III :wub:

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I went back to a cache that I could find by using other means that I have founds with. Such as the maps on the "View Cache Details" pages, other clues and common sense :wub: The GPSr sent me about 300ft to the west. I ended up in the middle of the street of the neighborhood next to the park that the cache is in :D I also went to anther cache I did find. The cell phone I just bought with the Geocache Navigator™ installed was reading right on the money. While the GPSr coordinates are constantly off by latitude minutes of 00.020 and longitude minutes of 00.080.

 

I would love to be able to find a way to check so I can have full confidence in the unit. Any help here would be very appreciated :wub:

 

If it maters its a Garmin GPS III :wub:

The problem with using caches to judge accuracy is there is the error from the GPSr of the person that placed the cache. One way to check is to go to the benchmark website and find a local benchmark. Let the GPS III sit for a while and compare the coordinates with those of the benchmark. Oh, and make sure you are using the same coordinate format as the benchmark.

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It sounds like the first thing you need to do is check which 'Datum' your GPSr is set for. It should be WGS84.

 

If you decide to use a benchmark to check your GPSr, be sure that the benchmark has "Adjusted Coordinates" and NOT "Scaled Coordinates". The benchmarks that have a Name usually have the adjusted coordinates, while those that have a number usually are scaled coordinates.

 

John

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The information provided in your post seems to indicate you are using the correct Geocaching Coordinate Format of DD:MM.mmm

 

Are you also set to the Geocaching Datum of WGS84 ?

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You also need to make sure you entered the coordinates using the correct system. Caches are listed using degrees and decimal minutes, dd mm.mmm. It is also possible to enter the coordinates into the GPS as degrees, minutes, and seconds, dd mm ss. If the GPS is set to accept dd mm ss, and you put in dd mm.mmm, it will take you to the wrong place.

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It sounds like the first thing you need to do is check which 'Datum' your GPSr is set for. It should be WGS84.

 

If you decide to use a benchmark to check your GPSr, be sure that the benchmark has "Adjusted Coordinates" and NOT "Scaled Coordinates". The benchmarks that have a Name usually have the adjusted coordinates, while those that have a number usually are scaled coordinates.

 

John

 

I checked the coordinates, I'm 99.99% sure I'm comparing apples to apples.

 

OK, I'll check my 'Datum'. Hmmmmm :D How, what & where is a 'Datum' on my GPS? I looked in the manual and don't see anything about that. I may know as something else.

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Try page 82 of the .pdf manual here. Set-up>>Position Settings>>Map Datum. If I were a betting man, I'd put money that it is set to NAD27 or something other than WGS84. Change it back and you'll be good to go.

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Thanks Sputnik 57 and others for the info. I'll try Position Settings and see what happens.

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Dear Mr. 2oldfarts (the rockhounders)and others,

 

I'm writing this post to inform you that in fact you were right about the "Datum" setting in my GPSr. After consulting with the owners manual, Indeed the "Datum" was set to a another setting then the default setting of WGS 84. After a few minutes of quality time with my GPSr, hopefully were good to go. Time will tell.

 

Stopped at one cache I haven't been able to find on the way home from work this morning. Checked the coordinates to as listed by the hider, they are right on the money ;) Still can't find the micro cache :rolleyes: I'll go back when I'm rested and in good day light :huh:

 

Thanks

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Thanks again for the help. The "Datum" setting was the ticket, I don't understand it, but its now puts me within a few feet of a cache. :D

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Thanks again for the help. The "Datum" setting was the ticket, I don't understand it, but its now puts me within a few feet of a cache. :D

 

A datum is a mathimatical model of the earth. They vary from one datum to the other.

 

N 111d 222.222m W111d22.222m describes a point on this earth. A cache for example

 

However because of differences between datums that same exact coordinate will describe a different point.

 

Thats why when the cache is WGS84 for it's datum and the GPS was set for another datum (NAD27 in the GPS most likely) the point was 300' off. Same coordinate used but different locations.

 

Reversing this.

Each datum would describe the same point on the earth using a slightly different coordinate.

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