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If you are placing a cache you must use your GPS to get the correct coordinates. The geocaching website uses coordinates in decimal degrees - HDDD° MM.MMM - which look like this N56°10.240 W003°22.260. Some of the interactive maps available to check locations to see if they are in nature reserves or other environmentally sensitive locations need coordinates in the Ordnance Survey British Grid Reference. Some landowners may also request coordinates in this format. This divides the UK into 100Km grid squares each with a two letter identification and then within each square a 6 or 10 digit number giving the eastings and northings. A grid reference looks like this NT1479398699 (or this NT147986 if it's only 6 digits NT147986). For The 10 digit number gives an accuracy on the map to 1 meter, the 6 digit reference gives an accuracy on the map to 100 meters. For more information about the OS GB grid click here (PDF document download).
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