Hi Sue,
Found that the following definition to be the most comprehensive - "GPS ( Global Positioning System ) satellite navigation units are hand-held receivers that pick up signals from satellites circling the earth, processing the information to give a read-out as a grid reference and an altitude to an accuracy of around 20m. They can be pre-programmed with a series of points along the route and will work out the bearing and distance required to reach them. However, they are not a substitute for traditional navigation and route-planning skills, which are in any case required to use GPS most effectively. Unlike compasses, GPS systems can run out of battery power and may lose satellite contact in bad conditions."
Never used one myself as I love to plan a route in detail using the guides ( Rucksack of couse ) and maps. Always carry the 'old faithful' compass.
However, I was researching a similar theme and used the Ramblers web site to see if they had a gps thread going in their forums and came across
www.ramblers.co.uk/forum/viewtopic.php?t=5036 Interesting reading in that there's a feeling that it's used as a back-up in case of problems rather than the other way round.
Be great to have our own thread running but the above may help in the short term.
Roy.