@conference{169,
  author = {L. Nelson and Judah Levine and P. Hetzel},
  title = {Comparing primary frequency standards at NIST and PTB},
  year = {2000},
  month = {2000-06},
  publisher = {IEEE},
  address = {Kansas City, MO, USA},
  doi = {10.1109/FREQ.2000.887426},
}