Official websites use .gov
A .gov website belongs to an official government organization in the United States.
Secure .gov websites use HTTPS
A lock (
) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.
Time Realization
Time and Frequency Realization
Coordinated Universal Time, abbreviated as UTC, is the official, internationally agreed upon standard for world time. NIST’s own representation of UTC, called UTC(NIST), serves as the official time and frequency standard for the United States. UTC(NIST) consists of a large group of continuously running atomic clocks, whose outputs are combined with weighted average techniques to form a single clock. UTC(NIST) agrees with UTC to within a few nanoseconds, and its frequency is periodically calibrated with state-of-the-art primary microwave and optical frequency standards that were designed and built by NIST.
