Abstract
The Japan Standard Time (JST) is calculated from the ensemble of the cesium atomic clocks at NICT Koganei headquarters. JST had a problem that the frequency of the timescale greatly changed by exiting of a clock from the ensemble. We found that the improper presuming method of the clock rate was the cause of this problem. We changed the presuming method so as to reflect the current performance of clocks, and the frequency change at the clock exiting was improved. We also confirmed the relation between the rate of exiting clock and frequency change of the time scale theoretically. It helps us to estimate the influence of the clock exiting.
