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:-
The horizontal axis must be perpendicular to the vertical axis.
The vertical circle must read zero when the line of collimation is horizontal.
The axis of altitude level must be parallel to the line of collimation.
The line of collimation or line of sight should coincide with axis of the telescope.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.
The axis of plate levels must be perpendicular to the vertical axis.