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Precise Time

The U. S. Naval Observatory is charged with maintaining the DoD reference for Precise Time and Time Interval (PTTI).  That reference is UTC(USNO).

You can contact us about timing products through our contact pages.

USNO Master Clock

The DoD common time reference is the U.S. Naval Observatory Master Clock.  It is generated at USNO in Washington, D.C. and at the Alternate Master Clock Facility at Schriever AFB in Colorado.


USNO monitors the GPS constellation and provides system timing offsets to 2SOPS, timing data for individual GPS satellites, and time transfer services using GPS.

Computer Display Clocks

USNO servers provide a wide variety of web-based time synchronization products including embedded web clocks to display UTC(USNO) on other web pages.


The highest precision and accuracy in time dissemination is provided through Two-Way Satellite Time Transfer (TWSTT).  USNO provides operational time transfer and calibration services for TWSTT.

Telephone Time

USNO provides both voice announcements of the time, and services to synchronize systems over telephone modems.


Network Time Protocol (NTP) is an Internet standard that enables client computers to synchronize to USNO.  NTP runs as a client program on a computer.



USNO Master Clock Time
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