@conference{4476,
  author = {D. Allan and D. Davis and Judah Levine and M. Weiss and N. Hironaka and D. Okayama},
  title = {New inexpensive frequency calibration service from NIST},
  year = {1990},
  publisher = {IEEE},
  address = {Baltimore, MD, USA},
  doi = {10.1109/FREQ.1990.177488},
}