The NIST Time and Frequency Division maintains the UTC(NIST) time scale, which is crucial for navigation, communication, and scientific research. The BIPM’s Circular-T publication records the time differences between UTC and UTC(NIST). NIST scientists adjust UTC(NIST) by analyzing data from various sources, including BIPM information, satellite time transfer, and atomic frequency references.
The scientists aim to minimize the absolute time error between UTC and UTC(NIST) while maintaining frequency stability. Despite limitations due to clock and time transfer noise, NIST adjustments typically keep the root-mean-square deviation of UTC – UTC(NIST) within 3 ns and frequency instability below 2 × 10^-15. Over long averaging intervals, both measures are significantly lower, with rate instability approaching the uncertainty limits of the world’s best primary frequency references.
Keywords: Time, Frequency, Metrology, Uncertainty, Stability
