Role of the BIPM in UTC Dissemination to the Real Time User

The generation and dissemination of International Atomic Time, TAl, and Coordinated Universal Time, UTC, are explicitly mentioned in the list of the principal tasks of the BIPM, that appears in the Comptes Rendus of the 18e Conference Generale des Poids et Mesures, in 1987. These time scales are used as the ultimate reference in the most demanding scientific applications and must, therefore, be of the best metrological quality in terms of reliability, long-term stability, and conformity of the scale interval with the second, the unit of time of the International System of Units. To meet these requirements, it is necessary that the readings of the atomic clocks, spread all over the world, that are used as basic timing data for TAI and UTC generation, must be combined in the most efficient way possible. In particular, to take full advantage of the quality of each contributing clock calls for observation of its performance over a sufficiently long time. At present, the computation period treats data in blocks covering two months. TAI and UTC are thus deferred-time time scales that cannot be immediately available to real-lime users. The BIPM can, nevertheless, be of help to real-time users. The predictability of UTC is a fundamental attribute of the scale for institutions responsible for the dissemination of real-time time scales. It allows them to improve their local representations of UTC and, thus, implement a more thorough steering of the time scales diffused in real time. With a view to improving the predictability of UTC, the BIPM examines in detail timing techniques and basic theories in order to propose alternative solutions for timing algorithms. This, coupled with a recent improvement of timing data, makes UTC more stable and, thus, more predictable.