Universal Deluxe 13 1/2" Indoor/Outdoor Atomic Clock, 13.5" Overall Diameter, Black Case, 1 AA (sold separately) - A fully sealed, weather-resistant case and large, easy-to-read numerals on its face make this clock ideal for high-humidity, outdoor environments. As it maintains radio contact and automatically synchronizes with the National Bureau of Standards' atomic clock in Boulder, Colorado, it can be relied upon for up-to-the-minute accuracy and precision. For added convenience, it also automatically syncs up with Daylight Savings Time changes within the continental US time zones: Eastern (EST), Central (CST), Mountain (MST) & Pacific (PST).