@misc{indiciaeafff34d9ad40,
  title = {Portable equipment for borehole exploration},
  author = {A.I. Johnson},
  year = {1963},
  doi = {10.3133/ofr6365},
  url = {https://pubs.usgs.gov/publication/ofr6365},
  note = {Source identifier: ofr6365}
}