Diopter ruler

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Diopter ruler with compass
Diopter ruler on a tripod

The diopter ruler , also known as the crocodile device , is the forerunner of the tilting rule . It is a ruler on which a rear sight in the manner of two vertical rails, each with a slot or sliding panels (discs with a fine hole) is attached.

The diopter ruler, like the tilting rule, which is equipped with a telescopic sight, was used to graphically record polar coordinates for geodesy and measurement on a measuring table . The accuracy is limited and cannot be compared with that of a tilt rule. The diopter ruler is, however, quite suitable for creating simple and quick sketches .

Diopter rulers are only occasionally manufactured and offered. They are then mostly used for training and as an inexpensive substitute for the (now rarely used) tilting rule when creating simple sketches , for example in archeology and speleology .


  • Johann Georg Krünitz: Economic Encyclopedia. 60th part, Brünn 1795, p. 693 "The movable diopters ..." full text in the Google book search
  • August Schulz Montanus: Systematic manual of the entire land and earth measurement with plane and spherical trigonometry also description of the newer usable measuring instruments. Vol. 1, August Rücker, Berlin 1819, p. 182 "Diopter ruler (Visir ruler)". Full text in Google Book Search
  • Diopter ruler. In: Pierer's Universal Lexicon. Volume 5, Altenburg 1858, p. 168. Diopter ruler at Zeno.org .