@article{206946,
  author = {Michael Lombardi and Thomas Heavner and Steven Jefferts},
  title = {NIST Primary Frequency Standards and the Realization of the SI Second},
  year = {2007},
  number = {2},
  month = {2007-12-01},
  publisher = {Measure: The Journal of Measurement Science},
  url = {https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=50602},
  language = {en},
}