Recommendation 3 of the 17th CCTF (2006)

Concerning the use of measurements of the International Atomic Time (TAI) scale unit

The Consultative Committee for Time and Frequency (CCTF),

considering that

• the number of primary frequency standards (PFS) reporting measurements of the TAI scale unit has significantly increased and is expected to continue doing so,
• in the future, secondary representations of the SI second are also expected to report measurements of the TAI scale unit,
• Recommendation CCTF 2 (2004) provides guidelines for reporting such measurements, and recommends that the Working Group on the Expression of Uncertainties in Primary Frequency Standards (at present the Working Group on Primary Frequency Standards) reviews the use of all reported evaluations of PFS,
• the first measurements from a new PFS might exhibit excessive frequency excursions that tend to disappear as more experience with the standard and the frequency transfer process is gathered,
• PFS sometimes undergo modifications leading to significantly changed characteristics and corresponding uncertainties;

recommends that

• the BIPM circulates to the Working Group on Primary Frequency Standards first reports of measurements from new standards, as well as those from frequency standards whose uncertainties have changed appreciably,
• the use and subsequent publication of those reports in Circular T be delayed to allow comments from the WG on PFS, following which, publication should be subject to a mutual decision by the concerned laboratory and the BIPM, and
• the long-term frequency stability of a new PFS relative to TAI should be evaluated over several months prior to the submission of a first report, and such data should be included in this report.

DOI : 10.59161/CCTF2006REC3E