Permanent adjustments of theodolites

The permanent adjustments of theodolites are made to establish fixed relationship between the instrument's fundamental lines. The fundamental lines or axis of a transit theodolite include the following:-

These adjustments once made last for a long time. These are important for accuracy of observations taken from the instrument. The permanent adjustments in case of transit theodolite are:-

  • Horizontal axis adjustment.

The horizontal axis must be perpendicular to the vertical axis.

  • Vertical circle index adjustment.

The vertical circle must read zero when the line of collimation is horizontal.

  • Adjustment of altitude level.

The axis of altitude level must be parallel to the line of collimation.

  • Collimation adjustment.

The line of collimation or line of sight should coincide with axis of the telescope.[1] The line of sight should also be perpendicular to the horizontal axis at its intersection with the vertical axis . Also, the optical axis, the axis of the objective slide, and the line of sight should coincide.

  • Adjustment of horizontal plate levels.

The axis of plate levels must be perpendicular to the vertical axis.[2]

See alsoEdit


  1. ^ Surveying by Dr. B.C Punmia and Dr Ashok Kumar Jain
  2. ^ surveying volume 1 by Prof. C.L Kochher, page no. 340 and 341.