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19th century articulated bronze theodolite for land surveying...
h : 20 cm
d : 7.8 cm
A theodolite is an optical instrument that measures angles in both horizontal and vertical planes. It is used to measure the angles of a triangle.
It is an essential instrument in geodesy, cartography, topography, engineering and archaeology.
Surveyors use it as their main field instrument.
A theodolite is a telescope mounted on both vertical and horizontal axes. Each axis is equipped with a graduated circle for angle readings.
The theodolite is placed on a support and must be aligned horizontally. It is often placed on a tripod, and aligned exactly vertically to a known point using a plumb line and a spherical spirit level. Its base must be perfectly horizontal. This whole phase of use is called "setting up". In fact, it is the instrument's main (vertical) axis of rotation that is made perfectly vertical with the help of the levels. The ground station point is perfectly aligned with this main axis. The telescope's second axis of rotation is made perpendicular to the main axis by internal adjustment. It will therefore be perfectly horizontal.
Ref: FQOA79M96M