The global positioning system (GPS) is a network of satellites and receiving devices that is used to determine the location of something on Earth. Some GPS receivers are so precise that they can pinpoint their location to within 1 centimeter (0.4 inches). GPS receivers provide location information in the form of latitude, longitude, and altitude. They also provide accurate time.
GPS consists of 24 satellites that circle the Earth in precise orbits. Every 12 hours, each satellite completes a full orbit of the Earth. These satellites are constantly broadcasting radio signals.
GPS receivers are programmed to receive information about where each satellite is at any given time. A GPS receiver determines its own location by measuring the time it takes a signal from at least four satellites to arrive at its location. Because