Tinkers

GPS stands for Global Positioning System.   The GPS uses a constellation of satellites (as of March 2008, there were 32) that transmit a certain signal, allowing GPS receivers to determine their location, speed, direction, and the exact time. 

Originally developed by the United States Department of Defense, GPS systems have become part of navigation, map-making, land surveying, commerce, and use by private citizens.  GPS also provides a reference for the precise time, aiding in the scientific study of earthquakes and the synchronization of telecommunications networks.