Our Atomic Watches automatically set themselves to radio signals linked to the U S Atomic Clock so youll always know the exact time Precision time is achieved by the watchs built in receiver that tunes in daily to the National Institute of Standards and Technologys Atomic Clock in Boulder CO Accurate to within a ten billionth of a second the Atomic Clock sends the signal directly to the watch keeping you on time every time Features 100 Feet Water Resistant Black and Gray Plastic Construction Moonglow / Dayglow Digital Display