Time and frequency can be transferred via a number of techniques depending on the accuracy required. The primary means of accurate time transfer is the global positioning system (GPS). GPS uses a constellation of satellites each containing atomic clocks. These spaceborne atomic clocks, combined with the monitor station caesium standards establish GPS time, the system synchronization time. Using GPS for time and frequency dissemination relies upon the stability and precision of GPS time for positioning. Simultaneous passive reception of multiple GPS satellites requires the satellites to be precisely synchronized to each other with less error than that expected from the individual satellite pseudorange measurement with the user receiver. The stability of the individual satellite clock between updates or re-synchronization with GPS Time, determines the system synchronization error.