Discussion on the calculation of the uncertainties of [UTC-UTC(k)]

Abstract

Coordinated universal Time UTC is the reference timescale generated by the BIPM and is made available through the published values [UTC–UTC(k)]. In a previous paper, Panfilo et al (2020 Metrologia57 065011) we examined the calculation of the uncertainties of [UTC–UTC(k)] and proposed some evolution to the current procedure. We here complete and clarify two main issues related to this calculation that have appeared in discussions and publications following our previous paper. We state (i) that the systematic uncertainty for a specific laboratory UTC(k) is not affected by biases from other laboratories and (ii) that the uncertainties of [UTC–UTC(k)] only depend on the input covariance of the epoch. We highlight the role of UTC and of the uncertainties of [UTC–UTC(k)]. Based on the present computation algorithm ALGOS, we detail internal procedures of the BIPM Time Department implementing the algorithm to ensure the continuity of UTC when changes occur e.g. a new laboratory entering UTC or a new calibration introduced in a specific receiver/time link.