There are two federal agencies that offer very accurate time signals by telephone, and one of them offers shortwave radio broadcasts of the same information.
Dialing the United States Naval Observatory Master Clock at (202) 762-1401 puts you in touch with a time signal in hours, minutes and seconds, on a twenty-four-hour clock in Eastern daylight or standard time, followed five seconds later by the Coordinated Universal Time, calculated for the Greenwich meridian, at zero degrees longitude.
The call is billed at regular long-distance rates.
Another source of time, the Division of Time and Frequency of the National Institute of Standards and Technology at Boulder, Colorado, is one of the sources of Coordinated Universal Time.
Time scales calculated by timekeeping agencies all over the world were fed into the International Bureau of Weights and Measures in Faris and averaged; the result is Coordinated Universal Time.
The National Institute of Standards and Technology, an agency of the United States Department of Commerce, is the source of official time in the United States.
It maintains its own atomic clock, which determines the time based on vibrations of the cesium atom. A second takes exactly 9,192,631,770 vibrations.
Calling (303) 499-7111 reaches the institute’s Coordinated Universal Time signal.
The identical signal is heard on the agency’s radio station, broadcasting at shortwave frequencies of 2.5, 5,10, 15 and 20 megahertz.
The time delay involved in the telephone transmission would vary according to how the call was switched, but would not exceed 70 milliseconds. In setting a wristwatch, the time delay would be so small you probably couldn’t calculate for it.
Irregularities in the earth’s spin require adding an occasional leap second.
So for those interested in an even more precise time, the station also broadcasts coded information, heard in the double tick of the first fifteen seconds of each minute, that tells the caller how far from Universal time the earth time is for any particular moment.
Earth time changes, atomic time doesn’t.
The easiest way these days is to sync your watch if you still have one, with a computer or cell phone.