On 9 June 2023, Circular T no. 425 published by the BIPM Time Department featured, for the first time, a comparison of local time scales UTC(k) using measurement data obtained from Galileo, the European Global Navigation Satellite System.This type of measurement is one of the fundamental steps used to compare atomic clocks from around the world in order to compute Coordinated Universal Time (UTC). Each UTC(k) time scale is measured with more than one technique to ensure redundancy and to provide the possibility to crosscheck and detect potential faults. The most stable and recently calibrated technique is then chosen as official, while all others are used as backup for monitoring purposes. The time comparison techniques used in UTC, starting with 1990, are based on Global Navigation Satellite Systems such as GPS and GLONASS, and later on the TWSTFT/SDR.

More recently, measurements based on Galileo have been introduced as a backup. Work is in progress for the calibration and characterization of BeiDou and optical fibre measurements for their full exploitation. For the computation of Circular T no. 425, one of the contributing laboratories was officially compared by using the Galileo measurements which were the most reliable for the month. The use of Galileo and the envisioned integration of other techniques is of major significance. The redundancy of measurement methods enables the detection of sudden anomalies or gradual long-term drifts, thus improving reliability and accuracy in the computation of UTC.

UTC time laboratories are compared by different techniques.