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NIST Updates Popular Guide to Radio-Controlled Clocks

The National Institute of Standards and Technology (NIST) has updated its popular guide to radio-controlled clocks. Many millions of radio-controlled clocks, watches, and other timepieces are automatically synchronized to official NIST time through special NIST radio broadcasts. The guide is intended to help manufacturers develop reliable and usable radio-controlled clocks, and help consumers select appropriate products, learn how they work, and troubleshoot reception problems.

In the United States, the signals received by radio-controlled clocks originate from NIST Radio Station WWVB, located near Fort Collins, Colo. When working properly, radio-controlled clocks always display the correct time and date, down to the exact second, and never require adjustments. Radio-controlled clocks are automatically updated for such changes as Daylight Saving Time, leap years, and leap seconds.

The updated guide contains a number of changes, including the revised rules for Daylight Saving Time, corrections in time zone tables, and several new recommendations for manufacturers. The guide also lists the latest WWVB specifications, several of which were changed—broadcast power was boosted, for instance—to make radio-controlled clocks work better.

The guide is among NIST's most requested publications. Each year, the guide is downloaded from the NIST web site about 100,000 times, and an additional 500 hard copies are disseminated.

WWVB Radio Controlled Clocks: Recommended Practices for Manufacturers and Consumers (2009 Edition) is available online at You may also receive a printed copy by sending your mailing address to sp960 [at] (sp960[at]boulder[dot]nist[dot]gov) or calling (303) 497- 4343.

Released September 22, 2009, Updated January 23, 2023