Coordinate variance between units

[+Pat in Louisiana]

I’ve been curious about how much variance there is in the hand held units.

Has anyone ever logged a cache that asked you to mark a waypoint and post it?

I think I just might do that and see what the numbers turn out to be.

Might do a “scatter plot type of chart” and update it periodically as the finds come in.

[+uxorious]

Here is one. GCVZC7

 

I suspect weather and atmospheric conditions have more to do with the differences. On any given day, if caching with others, there doesn't seem to be a consistent difference between individual units.

 

When I would use my Magellan, and my brother his Garmin, we would sometimes find the readings between them a little different, but neither seemed more accurate then the other. I got a Garmin CSx for Christmas, and I love all the added features. However, other then maybe getting a better signal in the trees, it doesn't find any more caches then my old unit. Just way easier to use. (MY Magellan is an explorist 210, great unit, but not as great as my new Garmin. )

[+StarBrand]

Try going Geocaching with 4 friends all with different units and compare readings - you will be shocked!!

 

I've seen 3 identical units laid next to each other with a clear view of the sky give readings as much as 18 feet apart.

[+Pat in Louisiana]

I know what you meen.

My wife's Colorado and my Oregon are up to 50 feet off on some days

(her's is closer to the caches)

[knowschad]

At an event a couple of years ago, the host gave a set of coordinates and a little surveyor's flag to each cacher, had them go to those coordinates, and stick their flag in the ground. We made our own scatter chart, and boy! were they scattered!

 

And we all had the same "weather and athospheric conditions" (although the GPS folks tell us those don't matter), the same degree of bounce, etc.

[+Ramona Retired Snipe]

I was at an event this spring and one of the parts of the event was to check your GPSr for accuracy. You were given a small flag (surveyors type) and a coordinate within the event site. There was 20 sq foot area with flags of all the participants. One flag ended up over 25ft away from the concentration (never did find out whose flag it was), even though it was in a clearing with no cloud cover. Even mine only gave me plus or minus 10 feet using a Garmin GPSMAP 60cx

[+wimseyguy]

Calibration Station is near a benchmark that has pretty accurate coords.

Check out the gallery to see the degree of accuracy of the finders who bothered to post a pic. Quite a wide range of numbers and equipment.

[+tec_64]

Here's something I did that is sort of relates:

 

http://www.personainternet.com/mile77/3709562.htm

 

tec_64

[+PhxChem]

My favorite "experience" on this subject has to do more with the user than the GPSr. It's something you might see in the logs....

 

It's the unwavering belief that your (whoever you may be) GPSr must be the "correct" one.

 

I get these: coordinates off by 20 ft. Followed by: coordinates spot on.

 

Who is correct? Who knows. I'm smart enough to know (or at least I tell myself) that the day I hid my geocache, my unit might have been a little off...

[+Isonzo Karst]

Our event experience was the opposite of knowschad.

 

At an event of ours we had a surveyor friend use his equipment to generate coords for a penny in a baseball field. We surveyed in from a benchmark on a nearby bridge.

 

We then gave every one the coords (rounded up from those that the Trimble equipment generates) and flags. Most units were within the area that is described by a thousandth of a minute. There were a couple of extreme outliers, most likely from misloading the coordinates. Open sky.

 

I think operator error, satellite geometry and atmospheric conditions are more critical than brand name.

 

On the other hand, image below is of two identical Merigolds, loaded with the same coords, being carried by me one day... hard to see clearly, but one of them is reading 93 feet to GOTO and the other is reading 146 feet to the same set of coords.....

 

[+Kryten]

Even supposedly identical GPS units will give different readings because they maintain an internal table of temperature corrections which grows with time so older GPS receivers tend to be more accurate as a result. The temp data is deleted when a software reset is performed.