An Accuracy Algorithm for an Atomic Time Scale

The accuracy of the rate or frequency of an atomic time scale is the degree to which its unit agrees with the SI second. Primary frequency standards are constructed in such a manner that t,hey provide the most accurate possible physical realization of the SI second. These standards are then used to calibrate or construct an atomic time scale which may also be used as a stable reference standard. Mathematical models characterizing the performance of both the primary frequency standards and reference standards are developed, and based on these models a current best estimate of the SI second is derived utilizing current and previous calibrations. The modeling techniques and theory are applied to the NBS primary frequency standards and atomic time scale system and a significant improvement is realized in the accuracy of the frequency estimate so derived. We estimate that the second used by the Bureau International de 1’Heure in generating TAI and UTC was too short by about 9 ? 2 parts in 1013 during the fall of 1974.