@misc{indiciae07905e0a2f4b,
  title = {Marking techniques},
  author = {Daniel E. Varland and J.A. Smallwood and Leonard S. Young and Michael N. Kochert},
  year = {2007},
  url = {https://pubs.usgs.gov/publication/70211030},
  note = {Source identifier: 70211030}
}