@misc{indiciaeca49ac0fb3a6,
  title = {An improved "spinning top" for exposure timer checking coupled with a light beam checking device.},
  author = {J W Addy and P Harrison},
  year = {1969},
  doi = {10.1259/0007-1285-42-495-229},
  url = {https://pubmed.ncbi.nlm.nih.gov/5765701/},
  note = {Source identifier: 5765701}
}