Theodolite is a popular surveying instrument. It is a measurement tool with which we can find horizontal and vertical angles. It is an electronic device and has sophisticated parts. To learn theodolite surveying a surveyor must know all the parts of the theodolite machine. In the following article, major parts of a theodolite are discussed to make the device well familiar for the surveyor. 

Parts of a Theodolite

Knowing the parts of a theodolite is important. The parts should be accustomed to each other. Without regulation of the parts cannot be worked accurately. Whenever theodolite uses in sites, each part takes seriously. Depends on placing the parts, the measuring result could be changed or stabled. Theodolite consists of some main parts, such as:


  • Telescope
  • Horizontal plate (Circle)
  • Vertical Circle
  • Index frame
  • The standards
  • The upper plate
  • The lower pale
  • Plate level
  • The leveling head
  • The shifting head
  • Magnetic compass
  • Tripod
  • Plumb bob

These theodolite parts are discussed briefly below.

  • Telescope- It is used to see the object. It rotates about a horizontal axis in the vertical plane. It can be up to an accuracy of 20 degrees.
  • Horizontal plate (Circle)- It is used for measuring the horizontal angle.
  • Vertical Circle- It is used for measuring the vertical angle.
  • Index frame- The frame consists of horizontal and vertical wings. This frame is additionally called a t-frame or vernier frame. The horizontal wing helps to require the measurement of vertical angles and the vertical wing helps to grip the telescope at the wanted level.
  • The standards- Standards look like 'A' shaped and for that, it is known as A-frame. The standards’ frames support the telescope and allow it to spin about the vertical axis.
  • The upper plate- It is the bottom on that standard and vertical settled. It also helps to rotate the standards and telescope regularly for correct measurement. the upper plate must be horizontal to the alidade axis and coordinate to the trunnion axis. The instrument must be leveled and this leveled is achieved by adjustment of three-foot screws and perceptive an explicit tube bubble. The bubble is understood as a plate bubble and located within the upper plate.
  • The lower pale- The lower plate is that the base of the entire instrument. It homes the foot screws and the carrying for the vertical axis. it is strictly connected to the tripod-escalating assembly and does not modifier or shift. Horizontal angles are measured with this plate.
  • Plate level- Plate levels are lifting by the upper plate that is the proper angles to every different with one they are coordinate to trunnion axis. Plate levels facilitate the telescope to mend incorrect vertical points.
  • The leveling head- The leveling head consists of two parallel triangular plates called tribrach plates. The upper one is called as upper tribrach plate and is used to level the upper plate and telescope with the help of equalizing screws provided at its three ends. The lower one is called a lower tribrach plate and is connected to the tripod stand.
  • The shifting head-Shifting head conjointly consists of two parallel plates that are modified one over the opposite among a limited range. Shifting head lies below the lower plate. It is helpful to centralize the complete instrument over the positioning.
  • Magnetic compass- A circular box compass or magnetic compass is mounted on the vernier scale between the standards. It is provided for taking the magnetic bearing points.
  • Tripod- The theodolite is mounted on a powerful tripod once getting used within the field. The tripod’s legs are sturdy or framed. At the lower ends of the legs, pointed steel shoes are provided to urge them pushed into the bottom. The tripod head has male screws on that the trivet of the leveling head is screwed.
  • Plumb bob- To center the instrument precisely over a station mark, a plumb bob is suspended from the hook fitted to the rock bottom of the central vertical axis.

The theodolite has other more parts are - Level tube, Foot Plate, Standard Frame, Upper Clamp, Trunnion Axis, Lower Clamp, Vernier Frame, Inner Axis, Outer Axis, Altitude Level, Leveling Screw, Clamp Screw. Tangent Screw



Please note that the information in is designed to provide general information on the topics presented. The information provided should not be used as a substitute for professional services.

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