This article needs additional citations for verification. (January 2021) |
The optical square uses a pentaprism to reflect and refract a beam or sighting 90 degrees, it is used in pairs in surveying and in a singular block in metrology.
In optical square A Horizon glass is placed at an angle of 120° with the horizon sight.
The Index glass is placed at an angle of 105° with the Index sight.
Angle between Index glass and Horizon glass is 45°.