This article explains how the National Institute of Standards and Technology (NIST) maintains precise time standards, such as NIST-F1, a highly accurate cesium fountain clock. NIST contributes to the international time scale by providing data to the BIPM (International Bureau of Weights and Measures). The AT1 scale at NIST is a real-time time scale that combines data from multiple atomic clocks to maintain stability. UTC(NIST), the U.S. version of Coordinated Universal Time, is based on AT1 but is adjusted periodically to align with the global UTC standard, using data from the BIPM.
The article also provides a table of parameters used to calculate the difference between UTC(NIST) and AT1 over specific months in 2008. These parameters include time offsets and frequency adjustments, which help ensure that UTC(NIST) remains accurate and synchronized with the global time standard. Leap seconds are also accounted for in these calculations, though they are not applied to the AT1 scale. The formulas and data allow for precise time comparisons and adjustments at any given moment.
Keywords: frequency standard, cesium fountain, UTC(NIST)
