Levelling

With three levelling screw the process of accurate levelling is as given below:

(i) Loosen the clamp and turn the telescope till the bubble axis is parallel to the line joining any two screws as shown in figure.

(ii) Until bubble is centred turn the two screws outward or inward equally and simultaneously

(iii) Turn the telescope by 90° so that it lies over the third screw as shown in fig and level the instrument by operating the third screw.

(iv) Turn back the telescope to its original position as shown in figure and verify the bubble. Repeat steps (ii) to (iv) until for both positions of the telescope bubble is centred.

(v) Rotate the instrument by 180°. Check the levelling.