GPS satellites (and now other global navigation systems commonly refered to as GNSS) include three or four atomic clocks that are monitored and controlled to be highly synchronized and traceable to national and international standards (known as UTC). So for time synchronization, the GPS signal is received, processed by a local master clock, time server, or primary reference, and passed on to "slaves" and other devices, systems, or networks so their "local clocks" are likewise synchronized to UTC. Typical accuracies range from better than 1 microsecond to a few milliseconds depending on the synchronization protocol. It is the process of synchronization to GPS that can provide atomic clock accuracy without the need for a local atomic clock. Still, local atomic clocks are sometimes desired as a long-term back-up solution to loss-of-GPS, either in the case or a weather-related outage, GPS interference, or other scenarios.
In any case, GPS clock synchronization eliminates the need for manual clock setting (an error-prone process) to establish traceability to national and international standards so various events can be correlated even when they are time-stamped by different clocks. The benefits are numerous and include: legally validated time stamps, regulatory compliance, secure networking, and operational efficiency.
