Recommendation 2 of the 12th CCL (2005)

Recommended frequency standard values for applications including the practical realisation of the metre and secondary representations of the second

The Consultative Committee for Length,

considering

• the significant advance and growth in absolute frequency values of optical frequency standards brought about by comb measurements;
• the differing accuracy requirements of the CCL length metrology community and the CCTF secondary representations criteria;

proposes that:

• the MeP-CCL list of Recommended Radiations and CCTF Secondary Representation list be combined into a single list of “Recommended frequency standard values for applications including the practical realisation of the metre and secondary representations of the second”;
• the CCL-MePWG and CCL/CCTF JWG be combined into a single CCL-CCTF frequency standards working group;
• the CCL may wish to select those frequencies which it considers important to highlight for use in high accuracy length metrology;
• other frequencies be proposed, evaluated and maintained on the frequency standards list by a CCL-CCTF frequency standards WG, but not necessarily accepted as CCL-preferred radiations or CCTF-accepted representations;
• the continued maintenance of such a frequency standards “category A” list from which the CCL and CCTF accepted values would be selected, together with the “category B” list representing those radiations still available for use, but where no further improvement in values and uncertainties was deemed necessary;
• the CCTF consider, evaluate and highlight those frequencies which it wishes to accept as secondary representations of the second;
• the schedule of CCTF and CCL meetings be rationalised to take place alternately, at appropriate intervals, ideally at a time of year close to but before the CIPM date;
• a meeting of the CCL-CCTF frequency standards WG should take place prior to the respective CC meeting if appropriate, in order to update the frequency list prior to consideration by the CC;
• the frequency values list is maintained on the BIPM website with version control, and is structured at a basic level according to wavelength and frequency value, but forms a database capable of being searched by accuracy level or by frequency or by wavelength.

DOI : 10.59161/CCL2005REC2E