@misc{indiciae6b5be45e2daf,
  title = {An improved optical backpointer for isocentric radiotherapy machines.},
  author = {J E Aldrich},
  doi = {10.1118/1.595529},
  url = {https://pubmed.ncbi.nlm.nih.gov/6482851/},
  note = {Source identifier: 6482851}
}