Determination of Allan deviation of Cesium atomic clock for lower averaging time

Absolute Allan deviation of the Cesium clock for averaging time (tau) of 5 days or more may be calculated from the corresponding data of Circular T published by Bureau International des Poids et Mesures (BIPM). For lower values of tau, the Allan deviation may indirectly be found from the extrapolation of these values through tau(-1/2) fit as recommended by CCTF-WGMRA guidelines. Absolute Allan deviation may also be directly found Out by inter-comparison Of minimum three clocks assuming that the noise in all clocks is fully uncorrelated. This paper analyses the values of Allan deviation determined by the direct method keeping in mind the limitation of the measurement system. These values of Allan deviation tally well with those found from the data of circular T.