US scientists debut NIST-F4, atomic clock that stays true for 100 million years straight.

• NIST scientists have published results establishing a new atomic clock, NIST-F4, as one of the world’s most accurate timekeepers, priming the clock to be recognized as a primary frequency standard — the ultimate source of time.
• The NIST-F4 clock was carefully and painstakingly assembled and tested over the last few years.
• By joining a small group of elite clocks run by a handful of countries, NIST-F4 makes the foundation of global time more stable and secure.