THE ACCURACY EVALUATION OF NIST-7

We have performed evaluations of the major systematic errors in NIST-7 with an overall uncertainty of less than a part in 10(14). The comple te evaluation process has been separated into two parts. With a comput er-controlled, digital servo system and some new measurement technique s, we now perform core evaluations (second-order Zeeman and Doppler sh ifts, cavity pulling and phase shift, line overlap and some electronic shifts) with an overall uncertainty of less than one part in 10(14) i n just a few days of measurements. The complete evaluation of all smal l and subtle effects in both the physics and electronics requires a fe w hundred days of data. But, these small effects are not variable at t he 10(-14) level and their infrequent evaluation does not detract from the operational accuracy of the standard.