Recommendation 3 of the 15th CCTF (2001)

The meaning of the designation "k" in UTC(k) and TAI(k)

The Consultative Committee for Time and Frequency,

considering that

• the International Bureau of Weights and Measures (BIPM) forms International Atomic Time (TAI) and, together with the International Earth Rotation Service (IERS), maintains Coordinated Universal Time (UTC) through the contributed timing data from institutes throughout the world,
• there is a need for a specific international notation for time scales to avoid all ambiguity as to their traceability to the international time references of the BIPM,
• Recommendation ITU-R TF.536-1 (1978, 1998) “Time Scale Notations” has established notation UTC(k) for time scales realized by institute “k”;

concurs with Recommendation ITU-R TF.536-1 (1978, 1998) “Time Scale Notations”; but

recommends that henceforth the designation of the institute “k” refers only to those institutes that participate in the formation of TAI and appear in Section 1, [UTC – UTC(k)], of the monthly BIPM Circular T;

requests the Director of the BIPM to write to the Director of the ITU-R to notify ITU-R of the recommendation above, and to seek ITU-R consideration for the adoption of nomenclature TAI(k) analogous to that of UTC(k).

Notes appended to Recommendation CCTF 3 (2001)

1. The institutes participating in the formation of TAI are:
   1. the national metrology institutes and designated laboratories participating in the CIPM Mutual Recognition Arrangement (MRA) and
   2. other institutes and observatories of the Member States of the Metre Convention and Associates of the CGPM officially nominated to keep time scales for scientific, navigational or astronomical purposes.
2. It is suggested that TAI(k) be defined by the relation TAI(k) = UTC(k) + DTAI, where DTAI is the number of integral seconds specified by the IERS as being the difference between UTC and TAI.

DOI : 10.59161/CCTF2001REC3E