Abstract. The primary clocks CS1, CS2 and CS3, and the new fountain clock CSF1 of the Physikalisch-Technische Bundesanstalt (PTB) have contributed to the realization of International Atomic Time (TAI) in 2000. With emphasis on the CSF1, operational data of the clocks are given together with the uncertainty with which they realized the second as defined in the International System of Units (SI). Results of comparisons of the realized second with the TAI scale unit are reported.

Print publication: Issue 6 (December 2001)