@misc{indiciaeaa7795cb662b,
  title = {Some effects of quiet geomagnetic field changes upon values used for main field modeling},
  author = {W.H. Campbell},
  year = {1987},
  doi = {10.1016/0031-9201(87)90144-0},
  url = {https://pubs.usgs.gov/publication/70014219},
  note = {Source identifier: 70014219}
}