GPS (System) Time
The time scale to which GPS signals are referenced. GPS Time derives from a composite or paper-clock consisting of all operational monitor station and satellite atomic clocks. It is steered over the long run to keep it within about 1 micro-second of UTC, as maintained by the Master Clock at the U.S. Naval Observatory, ignoring the UTC leap seconds. At the integer second level, GPS Time equalled UTC in 1980, but currently, due to the leap seconds that have been inserted into UTC, it is ahead of UTC by 10 seconds.