[moron4hire]

GPS satellites mostly just send out a timing signal. The receiving device then measures the differences between timing signals from the satellites it can see. This calculation is not simple, and lower power devices don't have the processing budget (or power budget, which is practically the same thing on a battery powered device) or don't have implemented as many error correction methods. For example, the signal echoing off of rock faces (or more often, buildings, for a more familiar environment), can make it look like one satellite is more than one satellite, which will obviously not give you the right location.