@article{9453,
  author = {D. Heddle},
  title = {A comparison of the \ etendue of electron spectrometers},
  year = {1971},
  journal = {Journal of Physics E: Scientific Instruments},
  volume = {4},
  pages = {589-592},
  month = {Jan-08-1971},
  issn = {0022-3735},
  url = {http://stacks.iop.org/0022-3735/4/i=8/a=009?key=crossref.d918105f8c7c6567b3af5eb5f9066b04},
  doi = {10.1088/0022-3735/4/8/009},
}