– the intergovernmental organization through which Member States act together
     on matters related to measurement science and measurement standards.
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Time services

    The BIPM Time Department provides a number of essential services for the large number of national metrology laboratories and timing centres around the world.

    • The BIPM Time Department calculates the international atomic time scale UTC and distributes it on a monthly basis through BIPM Circular T. Circular T provides official traceability to UTC for all the local (physical) realizations of UTC, UTC(k), and thereby allows the contributing time laboratories to steer their clocks to UTC. Currently more than 80 laboratories contribute clock and clock comparison data to UTC, meaning the BIPM interacts with them on a continous basis.

    • For those institutes participating in the CIPM MRA, their results are also published in the form of a key comparison, CCTF-K001.UTC, resulting in a monthly publication of the degrees of equivalence with respect to the reference time scale UTC.

    • 70% of the 80 laboratories also contribute data to the BIPM on a weekly basis, allowing the Time Department to calculate and distribute Rapid UTC (UTCr) every week, thereby allowing the participating laboratories to steer their clocks at shorter intervals.

    • The Time Department also distributes TT(BIPM) each year. This is a realization of Terrestrial Time, used mostly in scientific applications requiring long-term frequency stability and high frequency accuracy.

    • The Department maintains two international metrology resources: the FTP server of the BIPM Time Department, and the BIPM Time Department Database. Through these, laboratories maintaining timing services and users have access to detailed information relevant to the time scales.

    • The Department also manages the calibration of time transfer systems operated in the laboratories contributing to UTC; some of these are calibrated by the BIPM itself.

    In a typical year the BIPM Time Department manages 65 time scale comparisons with 45 to 80 participants, publishes several thousand files with clock and time transfer and time scale information, and coordinates and implements two or three calibration campaigns, visiting about ten laboratories. To fulfil its functions, the Time Department also interacts closely with several other organizations, some providing elements necessary for the time scale computation or time scale dissemination, and others representing large user communities. For more information please see http://www.bipm.org/metrology/time-frequency/liaisons.html.