Sat Nav devices can be useful but only if they are used in conjunction with road signs and a little common sense. Without this they can also be a disaster. One driver who was meant to be delivering cars from Turkey to Gibraltar ended up in a lane in Skegness after his sat nav device directed him towards a nature reserve called Gibraltar point. Of course the blame cannot be put solely on the sat nav device, presumably the driver is at fault for programming completely the wrong destination into it in the first place. And just for fun, here is a map showing the distance between the two destinations.
