Radio controlled clocks receive a signal from the NIST Radio station WWVB located near Fort Collins, Colorado. WWVB continuously broadcasts time and frequency signals at 60 kHz. WWVB provides standard time information, including year; time intervals; Daylight Savings Time, leap second, and leap-year indicators. The transmitted accuracy of WWVB is normally better than 1 part in 100 billion with day-to-day deviations less than 5 parts in 1000 billion.
Due to the effects of the many communication devices used throughout the United States (more so during the day than at night, and more so during the week than the weekend), the WWVB transmission is easier to receive at night and during the weekend.