@misc{1161381,
  author = {Allan S Risley},
  title = {The National Measurement system for time and frequency:},
  year = {1976},
  month = {1976-01-01 05:01:00},
  publisher = {, National Institute of Standards and Technology, Gaithersburg, MD},
  doi = {https://doi.org/10.6028/NBS.SP.445-1},
  language = {en},
}