Vertical axis

The vertical axis is the vertical axis of a theodolite to which one it when adjusting the horizontal angle turns.

It is implemented either as a cylinder axis in the substructure of the theodolite or as a ball bearing . If it is not exactly perpendicular , it is called a standing axis error . It is kept small by carefully leveling it with the help of a level and the three foot screws (between theodolite and tripod ).

Modern theodolites or total stations record the remaining amount of the standing axis error using an inclination sensor and correct the measurement accordingly with the aid of a compensator .