This article explains how the National Institute of Standards and Technology (NIST) maintains precise time standards using atomic clocks like NIST-F1, a highly accurate cesium fountain clock. These standards are used to contribute to international timekeeping efforts, such as UTC (Coordinated Universal Time), through the BIPM (International Bureau of Weights and Measures). NIST generates its own version of UTC called UTC(NIST) by adjusting the real-time AT1 scale, which is based on an ensemble of atomic clocks. This adjustment ensures that UTC(NIST) stays aligned with global time standards.
The article also provides details on how to calculate the difference between UTC(NIST) and the real-time AT1 scale using specific equations and parameters. These include offset values (x and y) for time and frequency, as well as leap seconds (xls). The process involves extrapolating from the most recent data provided by the BIPM. Changes to UTC(NIST) are made periodically, typically on the first day of each month, with adjustments limited to ±2 nanoseconds per day to maintain stability.
Keywords: frequency standard, time scale, atomic clock
