NIST-F2

NIST-F2 is a caesium fountain atomic clock that, along with NIST-F1, serves as the United States' primary time and frequency standard.

[1][2] NIST-F1, a cesium fountain atomic clock used since 1999, has a fractional inaccuracy (δf / f) of less than 5×10−16.

[3] At this planned performance level the NIST-F2 clock will not gain or lose a second in at least 300 million years.

[4] The evaluated accuracy (uB) reports of various primary frequency and time standards are published online by the International Bureau of Weights and Measures (BIPM).

[6] At the request of the Italian standards organization, NIST manufactured many duplicate components for a second version of NIST-F2, known as IT-CsF2 to be operated by the Istituto Nazionale di Ricerca Metrologica (INRiM), NIST's counterpart in Turin, Italy.

NIST physicists Steve Jefferts (foreground) and Tom Heavner with the NIST-F2 cesium fountain atomic clock, a civilian time standard for the United States.