Time and Frequency

  • Helmut Hellwig
  • David W. Allan
  • Fred L. Walls


In 1967 the General Conference on Weights and Measures adopted the cesium resonance frequency for the definition of the second. Universal Coordinated Time (UTC) has used a close approximation to the atomic second since 1972 (1). Time scales which refer to the rotation of the earth such as UTC are generated by inserting or leaving out seconds (leap seconds) at certain specified dates during the year, as necessary. This process is coordinated worldwide by the Bureau International de l’Heure (BIH). UTC is the de-facto basis for civil or legal time in most countries of the world (2). In addition to cesium beam standards, the atomic hydrogen maser has found use as primary frequency reference and clock.


Phase Noise Frequency Standard Phase Fluctuation Crystal Oscillator Fourier Frequency 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.


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Copyright information

© Springer Science+Business Media New York 1976

Authors and Affiliations

  • Helmut Hellwig
    • 1
  • David W. Allan
    • 1
  • Fred L. Walls
    • 1
  1. 1.Frequency & Time Standards SectionNational Bureau of StandardsBoulderUSA

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