@misc{indiciaef800ccb05f33,
  title = {Computation of geomagnetic transfer functions using the HP9640A},
  author = {David V. Fitterman},
  year = {1981},
  doi = {10.3133/ofr81361},
  url = {https://pubs.usgs.gov/publication/ofr81361},
  note = {Source identifier: ofr81361}
}