NIST Primary Frequency Standards and the Realization of the SI Second

  title={NIST Primary Frequency Standards and the Realization of the SI Second},
  author={Michael A. Lombardi and Thomas P. Heavner and Steven R. Jefferts},
  journal={NCSLI Measure},
  pages={74 - 89}
Abstract: As the base unit of time interval, the second holds a place of preeminence in the world of metrology. Time interval, and its reciprocal, frequency, can be measured with more resolution and less uncertainty than any of the other physical quantities. The precise realization of the second was made possible by the development of frequency standards based on the energy transitions of atoms, an event that not only revolutionized the science of timekeeping, but also forever changed many… 

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