Atomic Time Scales

The International Atomic Time (IAT) is a mean of local independent atomic time scales. The current procedure uses an algorithm ensuring the long-term stability, with fixed weights roughly proportional to the number of operating cesium standards. We found that the scale unit of IAT varied by probably less than 2 × 10-13 in relative value between January 1970 and December 1971. We tested some methods of weighting: they did not bring any substantial improvement. Our work suggests a more promising approach and also a means of maintaining both stability and accuracy.