A new atomic clock is one of the world’s best timekeepers, researchers say — and after years of development, the “fountain”-style clock is now in use helping keep official U.S. time. Known as NIST-F4, ...

BOULDER • Every second in a small laboratory room in Boulder, a green light flashes. Within the webs of yellow wire and shelves of computer systems, this green light represents the passage of time.

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 — ...