"How accurate is a radio-controlled clock?" National Institute of Standards and Technology (NIST) researcher Michael Lombardi asks and answers the question in a featured article of this month's Horological Journal, published by The British Horological Institute, Limited.
Often advertised as "atomic clocks," radio-controlled clocks get their sense of time by periodically checking the broadcast time signals from one of the world's major time-keeping agencies, which, to be fair, are synchronized with true atomic clocks. In the continental United States, such clocks generally use the 60 kilohertz signal from NIST's WWVB station in Fort Collins, Colo.
Lombardi explains that several factors affect the accuracy of your radio-controlled clock, including how accurate the radio station signal is, how long it takes the signal to reach your clock, how accurately your clock synchronizes with the signal, and how accurately it keeps time between synchronizations. On the whole, he says, it's reasonable to assume that at the time of synchronization the clock is probably accurate to within not more than 30 milliseconds—plenty good enough to make an appointment on time.
Read Lombardi's "How Accurate is a Radio Controlled Clock", the Article of the Month in the Horological Journal, at www.bhi.co.uk/aHJ/AOM.pdf. For more, see the NIST Web page WWVB Radio Controlled Clocks at www.nist.gov/physlab/div847/grp40/radioclocks.cfm or check WWVB Radio Controlled Clocks: Recommended Practices for Manufacturers and Consumers (NIST Special Publication 960-14, August 2009, PDF format) at http://tf.nist.gov/timefreq/general/pdf/2422.pdf.