Chicago Lighthouse - Atomic Slimline Clock, 12-3/4in, Black - Sold As 1 EachMaintains its accuracy by automatically matching the National Bureau of Standards Atomic Clock in Boulder, Colorado and automatically setting itself to daylight-saving time. Larger dial size makes it easier to tell time from a distance. Slimline design gives sleek, modern appearance. Body is biodegradable. Time Format: Standard; Power Source(s): 1 AA Battery (Sold Separately); Movement Type: Quartz; Overall Diameter: 12 3/4 in.Automatically matches the National Bureau of Standards Atomic Clock in Boulder, Colorado.Automatically sets itself to daylight-saving time.Larger dial size.Slimline design.Body is biodegradable.Includes hanging hardware.