Learn more about how time is measured.

What Time is It?
At the U.S. Time and Frequency Division of the National Institute of Standards and Technology
At the Time Service Department of the U.S. Naval Observatory
In Paris at the International Bureau of Weights and Measures
Japan Standard Time
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Organizations of Official Time
Time Service Department at the U.S. Naval Observatory
International Bureau of Weights and Measures in Paris
National Physical Laboratory in the United Kingdom
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The Technology of Measuring Time
Cesium Clock
Keeping Time with a Single Atom (The Optical Clock)
A History of Measuring Time
Measuring Time
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