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Practical realizations of the definitions of some important units
Recommended values of standard frequencies
SI Brochure: Appendix 2

The following values are recommended for applications including the practical realization of the metre (MeP) and secondary representations of the second (SRS).
In each case, reference is given to the relevant decision (CIPM, CCL or CCTF).


[Page last updated: 30 November 2018]
Note: All the radiations in the list (apart from the 87Rb 6.8 GHz transition) may be used for the practical realization of the metre (MeP).
Those radiations marked [SRS] may also be used as secondary representations of the second.

Graphical summary:

Background:

    The CCL-CCTF Frequency Standards Working Group was charged with producing and maintaining a single list of Recommended values of standard frequencies for applications including the practical realization of the metre and secondary representations of the second.
    The drop-down menu at the top of this page gives access to the list being developed by this group. Where full data sheets are not yet available, links are given to relevant decisions of the CIPM or CC.

Appendix 2 of the SI Brochure

The mises en pratique are prepared by the relevant Consultative Committees and are then published in electronic form here on the BIPM website, where they may be revised more frequently than if they were printed in the SI Brochure.

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