– the intergovernmental organization through which Member States act together
     on matters related to measurement science and measurement standards.
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FTP server of the BIPM Time Department
Circular T
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Hardware delay characterization
Annual Reports

TT(BIPM) is a realization of Terrestrial Time as defined by the International Astronomical Union (IAU). It is computed annually by the BIPM, based on a weighted average of the evaluations of the frequency of TAI by the primary and secondary frequency standards. It is mostly used in scientific applications requiring long-term frequency stability and high frequency accuracy.

Last computed TT(BIPMXY) and older computations can be accessed below :
(Each computation is identified by the string XY where 19XY or 20XY is the last year of data included)

Other international metrology data centres:

International metrology publications
SI Brochure
Guides in metrology
Circular T
Recommended values of standard frequencies
Related articles
International reference timescales
Recent publications of the BIPM Time Department