Yatchsmen, light aircraft pilots, drivers, mountaineers and walkers are all likely to benefit from new hand-sized instruments that can locate their position to within less than 100 metres. Wherever you are on the surface of the Earth, you need never be lost again. The system's precision is made possible because the instruments receive signals from one of the world's most sophisticated military satellite networks, the US Global Positioning System (GPS). It was the satellites of GPS that guided Allied troops and missiles with extraordinary accuracy in the Gulf War. Now civilian instruments little bigger than pocket calculators are available . And their current cost of several hundred pounds sterling looks set to tumble.