@book{Pfeiffer1997,
  author    = {Pfeiffer, Johann},
  title     = {HSP III Koordinatenmessger{\"a}t},
  publisher = {Fachhochsch.},
  address   = {Aachen},
  year      = {1997},
  language  = {de}
}
@book{Pfeiffer1997,
  author    = {Pfeiffer, Johann},
  title     = {Design und Herstellen von Werkzeugen mit Freiformfl{\"a}chen},
  publisher = {Fachhochsch.},
  address   = {Aachen},
  year      = {1997},
  language  = {de}
}