The Time Realization and Distribution group at NIST is responsible for maintaining and distributing the U.S. national standard for time and frequency, known as UTC(NIST). This standard is based on highly accurate atomic clocks, which measure time by counting the oscillations of signals tied to atomic transitions. NIST ensures the accuracy and stability of UTC(NIST) by regularly comparing it with primary frequency references and other national metrology labs. The group provides free access to time and frequency signals through various services like the Internet Time Service and radio stations, and offers specialized calibration services for those requiring higher accuracy.
In addition to supporting U.S. needs, NIST collaborates with the Sistema Interamericano de Metrologia (SIM) to maintain the SIM time scale (SIMT), a real-time, multi-national time standard that complements UTC. SIMT offers improved stability and close alignment with UTC, helping timing systems across the Americas. NIST is also developing a new Standard Reference Instrumentation (SRI) program to centralize its reference devices and support ongoing advancements in time and frequency metrology, including the use of optical atomic clocks.
Source: https://www.nist.gov/pml/time-and-frequency-division/time-services
Keywords: time metrology, atomic clocks, frequency references
