Theodolite

A theodolite is a precision instrument for measuring angles in the horizontal and vertical planes. Theodolites are used mainly for surveying applications, and have been adapted for specialized purposes in fields like meteorology and rocket launch technology. A modern theodolite consists of a movable telescope mounted within two perpendicular axes—the horizontal or trunnion axis, and the vertical axis. When the telescope is pointed at a target object, the angle of each of these axes can be measured with great precision, typically to seconds of arc.

Theodolites may be either transit or non-transit. Transit theodolites (or just "transits") are those in which the telescope can be inverted in the vertical plane, whereas the rotation in the same plane is restricted to a semi-circle for non-transit theodolites. Some types of transit theodolites do not allow the measurement of vertical angles.

There are different types of theodolite available. It may be classified into three broad categories.

*Vernier or Transit Theodolite
*Digital Theodolite
*Total Station

      Theodolites have many advantages when compared to other leveling instruments:

*Greater accuracy.
*Internal magnifying optical system.
*Electronic readings.
*Horizontal circles can be instantly zeroed or set to any other value.
*Horizontal circle readings can be taken either to the left or right of zero.
*Repeat readings are unnecessary.
*Theodolites have an internal optical device that makes reading circles much more accurate than other instruments.       Also, because the theodolite allows you to take fewer repeat readings, these measurements can be made much more quickly. Theodolites with optical instruments have advantages over other layout tools. They have more precise measurements, they are unaffected by wind or other weather factors, and they can be used on both flat ground and sloped ground.