@misc{indiciae008cf7fd465a,
  title = {An accurate, adjustable double shutter.},
  author = {M H Siegel and E Howard},
  year = {1967},
  doi = {10.2466/pms.1967.24.2.673},
  url = {https://pubmed.ncbi.nlm.nih.gov/6040247/},
  note = {Source identifier: 6040247}
}