How does Global Positioning System (GPS) time differ from Coordinated Universal Time (UTC)?
GPS time differs from UTC by the integer number of leap seconds that have occurred since the GPS time scale began on January 6, 1980. This difference equaled 13 seconds at the end of 2004.The integer-second difference is included in the GPS broadcast message, and is usually applied automatically so that GPS clocks display the same hours, minutes, and seconds as UTC clocks. GPS time also differs from UTC by a small number of nanoseconds (nearly always < 25 ns) that continuously changes. The small number of nanoseconds represents the difference between the GPS time scale on-time marker (OTM) and an estimation of the OTM for the UTC time scale maintained by the United States Naval Observatory, called UTC(USNO). The current difference between the UTC(USNO) estimate and GPS time is also part of the GPS broadcast message. GPS timing receivers generally apply this correction to their 1 pulse per second (pps) timing signals, so that the received 1 pps signal represents a real-time estimation o
