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Why The Difference?


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when im using my gps 60 in british OS mode i have one of the data fields showing me my current locaction in lat lon on the map page.

however, yesterday i was stood by the side of another gps. and my reading was different to his, however if i changed to lat lon mode they were identical.

 

im guessing it is chaging it so it fits with the map location. but surely this means im going to be off posistion when following lat lon locations.

 

or does the double error cancel it out?

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yeh, but if i have it in os mode, and i enter a cache using the data cable and easy gps, it always is spot on with the co ords. and always sends me to the correct location.

howerver as i said it says im at a different location to my friend on his, but we both aqre spot on.

i think it must cancel itself out, and even tho it looks wrong it is right.

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The confusion you are experiencing is due to the different display formats available on the GPS, not how the coordinates are stored inside. If you are using the data cable then the computer makes sure that the GPS knows the correct location, regardless of what display format / datum you happen to have chosen.

 

If you are in OS mode (OSGB datum), always use the British Grid format (eg SK 23456 83920), never lat/lon. If you really want to see lat/lon coordinates, ensure that you tell the GPS to use the WGS84 datum. Displaying lat/lon figures with an OSGB datum is always wrong, and it's plain bad design by the manufacturer if your GPS lets you do this!

 

The Geocaching.com website shows both WGS84 and OSGB coordinates so, for most caches, it doesn't matter which you prefer. "Walkers who also geocache" often leave their GPS in OS mode so that they can still use maps. "Cachers who just follow the arrow" without using maps are better off sticking to WGS84.

 

However, almost all multicaches and offset caches you come across will get you to do calculations with WGS84 lat/lon coordinates and enter them into your GPS, so you will need to change datum before you attempt any of these.

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