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Nouveau graphique illustrant l’exactitude du TAI et de l’UTC

A new tool is available from the Time Department, which allows the monitoring of the accuracy of the TAI scale interval with respect to realizations of the SI second by primary and secondary frequency standards (PSFS). The tool was developed with the support of Ms Nelida Diaz, a secondee from CENAM (Mexico). The plot reports the fractional deviation d over the last three years and the different PSFS input data can be inserted or excluded by clicking on the items in the legend.

The plot is automatically updated monthly and is available from the Time Department database at, reporting the data of Section 3 of Circular T. The monthly Circular T is available at

This tool will help with monitoring the mandatory criteria for the redefinition of the second (See Resolution 5 of the 27th CGPM (2022) “On the future redefinition of the second".