BIPM Circular T celebrates its 30th anniversary in 2018, having been published without interruption since 1 March 1988.
BIPM Circular T is the monthly publication produced by the Time Department that provides information on the offset between Coordinated Universal Time (UTC) and the local realizations UTC(k) maintained by national institutes. It also includes other information relevant to the computation of these values. When it was launched, the techniques for time comparison allowed the computation of values every ten days and Circular T presented time differences in microseconds for 39 laboratories spread over 24 nations. Today, Circular T provides the values of the differences [UTC - UTC(k)] every five days, for about 80 institutes that regularly contribute clock and clock comparison data to the BIPM.
BIPM Circular T is a dynamic publication and the quality of the results has increased progressively over the 30 years since it was introduced. This follows advances made with clocks and time and frequency transfer techniques by all Time Laboratories and in parallel with the constant improvement in the treatment of the data at the BIPM. The contents and presentation of Circular T have also evolved; from January 2016 an interactive HTML version gives access to complete information about the local time scales and the time links used for clock comparisons. In addition, all issues of BIPM Circular T, dating back to March 1988 and other useful information are available on the ftp server. https://www.bipm.org/en/bipm/tai/.