@misc{indiciaeb8770231bc91,
  title = {Device for spacing map contours},
  author = {L.J. Bjorklund},
  year = {1951},
  doi = {10.3133/ofr51101},
  url = {https://pubs.usgs.gov/publication/ofr51101},
  note = {Source identifier: ofr51101}
}