Multiple techniques have been developed, often transferring reference clock synchronization from one point to another, often over long distances.
In a two-way time transfer system, the two peers will both transmit and receive each other's messages, thus performing two one-way time transfers to determine the difference between the remote clock and the local clock.
The NIST provides a time reference service to computer users on the Internet,[5] based on Java applets loaded by each client.
The nature of the received signal is not important, although widely available timing and navigation systems such as GPS or LORAN are convenient.
[9] Since the advent of GPS and other satellite navigation systems, highly precise, yet affordable timing is available from many commercial GNSS receivers.
These distances combined geometrically with precise orbital information identify the location of the receiver.
GPS-based laboratory time references routinely achieve 10 ns precision.