When someone refers to GPS clock systems, they are talking about the new super-accurate radio transmitter operated clock systems. In order to work properly, It uses a synchronized by a radio-transmitted time code. The systems utilize satellite technology from the various satellites that are scattered in space around the earth, to record time with 100% accuracy. When a GPS satellite passes overhead, it sends time signals to the GPS receiver. The receiver then sends signals to a radio transmitter and it is rebroadcast to each clock that is programmed to be a part of the system. GPS is more accurate than any other RTCs. GPS systems can synchronize to within nanoseconds of the correct time. Where as RTCs provide accuracy in minutes. More..