@misc{indiciae761734fb810c,
  title = {Geomagnetic data utility programs for the HP9640A},
  author = {David V. Fitterman},
  year = {1981},
  doi = {10.3133/ofr81360},
  url = {https://pubs.usgs.gov/publication/ofr81360},
  note = {Source identifier: ofr81360}
}