The National Institute of Standards and Technology (NIST) has unveiled its latest atomic clock, NIST-F4, which is set to become one of the world’s most accurate timekeepers. The clock, located in Boulder, Colorado, measures an unchanging frequency in cesium atoms, providing a stable foundation for global timekeeping.
Established as one of the world’s most accurate timekeepers, NIST-F4 ticks at such a steady rate that if it had started running 100 million years ago, it would be off by less than a second today. The clock is based on a “fountain” design, which represents the gold standard of accuracy in timekeeping.
NIST-F4 joins a small group of elite timepieces run by just 10 countries worldwide, making the foundation of global time more stable and secure. Its improved time signals are used literally billions of times each day for tasks such as setting clocks and watches, and ensuring accurate time stamping of financial transactions.
The clock’s accuracy is comparable to the world’s best fountain clocks, with frequency measurements accurate within 2.2 parts in 10 to the 16th (10 million billion). The NIST team has taken months’ worth of measurements to ensure the clock’s stability and reliability.
NIST-F4 is part of a series of fountain clocks built by NIST, with two other clocks, NIST-F2 and NIST-F3, already operational. The new clock will be used to calibrate the NIST time scale UTC(NIST) and provide accurate time signals to the global timekeeping infrastructure.
The success of NIST-F4 has renewed NIST’s global leadership in primary frequency standards, with the agency’s director stating that the clock has “renewed our commitment to providing reliable and accurate timekeeping services.”
Source: https://www.nist.gov/news-events/news/2025/04/new-atomic-fountain-clock-joins-elite-group-keeps-world-time