The vertical axis of the instrument is made truly vertical by a leveling-up operation which can be completed according to the following steps. a three-foot screw arrangement of a dumpy level and show a four-foot screw arrangement of a dumpy level.
The telescope axis is placed parallel to the line joining one pair of screws .Both the screws 1 and 2 are rotated simultaneously by moving them equally inwards or equally outwards till the bubble of the spirit level on the telescope is brought to the centre of its run
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