Print 2018 marks the 30th anniversary of the publication of Circular T. Since March 1st, 1988 when Circular T was firstly published, National Time Service Center (NTSC) of the Chinese Academy of Sciences (CAS) has been providing data for it until now. And NTSC has gradually become the world's top three time laboratories in terms of long-term comprehensive performance.
NTSC has participated in TAI calculation since 1980, and has continued to provide data for TAI calculation and Circular T without interruption. Over the last 3 decades, China's UTC(NTSC) time reference system produced and maintained by NTSC has been continuously and stably operating and progressing. Its performance has been improved and functions has been expanded. At present, NTSC is one of the world's most important time laboratories for its essential role in TAI calculation, top-ranking weight contribution and internationally advanced performance.
Circular T is the monthly publication produced by the Time Department of BIPM that provides information on the offset between Coordinated Universal Time (UTC) and the local realizations UTC(k) maintained by national time institutes. Besides, it also includes other information relevant to the computation of UTC.
Currently, about 80 time institutes around the world regularly offer atomic clock and international time comparison data to BIPM. Circular T could provide value of [UTC - UTC(k)] every five days, and the quality of the results has increased progressively in parallel with the advance in atomic clocks and time frequency transfer technologies by world time laboratories and constant improvement in data treatment at BIPM.
