This article explains how the National Institute of Standards and Technology (NIST) maintains accurate time standards, particularly through its NIST-F1 cesium fountain clock, which is the U.S. primary frequency standard. NIST uses an ensemble of clocks, including cesium standards and hydrogen masers, to create the AT1 time scale, which runs in real time. UTC(NIST), the U.S. version of Coordinated Universal Time, is based on AT1 and adjusted using data from the BIPM (International Bureau of Weights and Measures). These adjustments happen monthly and are limited to keep time stability high.
The article also provides a table with parameters used to calculate the difference between UTC(NIST) and AT1 at any given time. These parameters include leap seconds, time offsets, and frequency adjustments. The data helps ensure that time measurements remain accurate and consistent across different systems and locations. The methods and algorithms used for timekeeping are based on research published over several decades, showing the long-term effort to improve time and frequency accuracy.
Keywords: frequency standard, cesium fountain, time scale
