@misc{indiciaec23f309eccc0,
  title = {International geomagnetic reference field 1980; charts and grid values},
  author = {Eugene B. Fabiano and N.W. Peddie and D.R. Barraclough and A.K. Zunde},
  year = {1983},
  doi = {10.3133/cir873},
  url = {https://pubs.usgs.gov/publication/cir873},
  note = {Source identifier: cir873}
}