@misc{indiciaec5f87674ac9e,
  title = {Secular, annual, and semiannual changes in the baseline level of the earth's magnetic field at North American locations},
  author = {W.H. Campbell},
  year = {2012},
  doi = {10.1029/jb085ib11p06557},
  url = {https://pubs.usgs.gov/publication/70012332},
  note = {Source identifier: 70012332}
}