The Atomichron was the world's first commercial atomic clock, built by the National Company, Inc. of Malden, Massachusetts. It was also the first self-contained portable atomic clock and was a caesium standard clock. More than 50 clocks with the trademarked Atomichron name were produced. See also Chip-scale atomic clock Hoptroff London References External links * A Brief History of the National Company, Inc Atomichron: The Atomic Clock from Concept to Commercial Product Atomic clocks