T: Centering error

P: Vertical collimation error, Horizontal collimation error, Eccentricity error

Explanation:

The following are some of the errors that are associated with a total station survey work:

A. Errors as those due to temporary adjustments (T) - Centering error

B. Errors as those due to permanent adjustments (P) - Vertical collimation error, Horizontal collimation error, Eccentricity error

Centering error: While centering, it is necessary to ensure the approximate levelness; otherwise, the centering will be disturbed when subsequent leveling of the instrument is done. It can be done by laser plummet.

Horizontal collimation error(or line of sight): This axial error is caused when the line of sight is not perpendicular to the tilting axis. It affects all horizontal circle readings and increases with steps sighting, but this is eliminated by observing two faces.

Vertical collimation error: A vertical collimation error exists on a total station if the 0⁰ to 180⁰ line in the vertical circle does not coincide with its vertical axis. It is eliminated by taking FL and FR readings.

Eccentricity error: It exists when the theoretical center of the mechanical axis of the theodolite does not coincide exactly with the center of the measuring circle. It is eliminated by measuring both faces.

Tilting axis error: These axial errors occur when the tilting axis of the total station is not perpendicular to its vertical axis. It is eliminated by two face measurements.