@misc{indiciaeb9a41f7b841a,
  title = {The magnetic field of the Earth, 1990: Vertical intensity chart},
  author = {N.W. Peddie},
  year = {1993},
  doi = {10.3133/gp1004z},
  url = {https://pubs.usgs.gov/publication/gp1004Z},
  note = {Source identifier: gp1004Z}
}