“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.
