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, ...

Researchers at the U.S. National Institute of Standards & Technology (NIST) say they have created the most accurate atomic clock to date — one that can measure time down to the 19th decimal place.

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.