@article{23843,
      author       = "Kehlen, Erhard and International Course Lasers in Surveying
                      and Construction, Stockholm 1973",
      title        = "Practical Experience in the Use of the AGA "Geoplane" 300 "
                      Laser Levelling Instrument  ",
      year         = "1973",
      note         = "1 sv.",
}