Angular Measurement
 Field Use of the
    Theodolite
 Taking Measurements
 Errors of Construction and
    Adjustment
 Collimation Error
 Horizontal Collimation
 Vertical Circle Index
 Plate Level
 Optical Plummet
 Miscentring
 Parallax in Telescope

Errors of Construction and Adjustment

Theodolites are instruments and are therefore susceptible to errors of both construction and adjustment. The effect of some of these errors can be ignored in the context of these reference notes however there are others that must be eliminated or reduced for the derived angle to have reliability. Luckily the method used for observing angles does this task.

All instruments, ranging from theodolites and levels to police radar and scales in the supermarket, are subject to errors of calibration and construction. Geomatic engineers are concerned with the effect of these errors on their measurements, and ways to compensate for any discrepancies.

The theodolite is subject to various errors which are listed below. These errors are caused by the manufacturing process and by changes in adjustment caused by time and use. There is not much that we can do regarding errors of construction, but for most applications these can be ignored as the manufacturers generally meet quite high standards. The errors in our angular observations caused by the state of calibration of the instrument can be reduced in the field by using the appropriate procedure, or compensated for in the reduction of the angles.

• Collimation Error
• Horizontal Collimation
• Vertical Circle Index
• Plate Level
• Optical Plummet
• Miscentring
• Parallax in Telescope