Performance of the PTB reconstructed primary clock CS1 and an estimate of its current uncertainty

The paper describes the current performance of the primary clock CS1 of the Physikalisch-Technische Bundesanstalt (PTB). The clock employs a thermal a tomic beam and magnetic state selection. After major reconstruction during 1995 and 1996, routine clock operation was restarted in May 1997. Results o f comparisons with UTC(PTB) and other internationally recognized time scale s are presented. An evaluation of the CS1 Type B uncertainty yielded 7x10(- 15) (1 sigma). The CS1 is thus the most accurate atomic clock in continuous operation world-wide.