Clocks receive signals from the United States Atomic Clock and automatically set themselves to the exact time. Recent breakthroughs in reception technology have made Atomic Clocks affordable for everyone. Our Atomic Clocks are set and kept accurate by the U S Government time signal in Boulder, Colorado. Computer codes inside our clocks set the clock to your time zone, from then on even the change from standard to daylight savings time takes place automatically. There has never been such a no fuss trouble free clock and talk of precise, the U. S. Atomic Clock is awesome measuring one second as 9,192,631,770 vibrations of a cesium-133 atom in a vacuum. Clocks require 1 "AA" battery. One year warranty. Real wood cherry finish 12.5" rim diameter.