Temporary adjustment of theodolite involves the subsequent steps. 1. Setting the Theodolite over the Station: The tripod stand is placed over the specified station. The theodolite is then lifted from the box and tighted on top of the stand by means of a wing nut or consistent with the fixing arrangement provided along side the instrument. 2. Approximate Levelling by Tripod Stand: The legs of the tripod stand are placed well apart and firmly fixed on the bottom . Then, approximate levelling is completed using this stand. to try to to this, two legs are kept firmly fixed on the bottom and therefore the third is moved in or out, clockwise or anticlockwise, in order that the bubble is approximately at the centre of its run. 3. Centring: Centring is that the process of setting the instrument exactly over a station. At the time of approximate levelling by means of the tripod stand, it should be ensured that the plumb suspended from the hook under the vertical axis lies approximately over the station peg. Then, with the assistance of the shifting head (movable capstan nut), the centering is completed accurately in order that the plumb is strictly over the nail of the station. 4. Levelling: Before starting the levelling operation, all the foot screws are delivered to the centre of their run. Then the subsequent procedure is adopted a. The plate bubble is placed parallel to any pair of foot screws (say the primary and second foot screws), By turning both these screws equally inwards or outwards, the bubble is delivered to the centre. b. The plate bubble is turned perpendicular to the road joining the primary and second foot screws. Then by turning the third foot screw either clockwise or anticlockwise the bubble is delivered to the centre. Some instruments may have two plate bubbles perpendicular to every other, In such a case, one bubble is kept parallel to any pair of foot screws; the opposite plate bubble will automatically be perpendicular to the position of the primary bubble. Here, the instrument needn't be turned. the primary bubble are often delivered to the centre by turning the primary and second foot screws, and therefore the second bubble are often delivered to the centre by turning the third foot screw.
c. The method is repeated several times, in order that the bubble remains within the central position of the plate bubble, both directions perpendicular to every other. d. The instrument is rotated through 360° about its vertical axis. If the bubble still remains within the central the adjustment of the bubble is ideal and therefore the vertical axis is actually vertical. 5. Focussing the Eyepiece: The eyepiece is focussed in order that the cross-hairs are often seen clearly. to try to to this the telescope is directed towards the sky or a bit of white book is held ahead of the thing glass, and therefore the eyepiece is moved in or out by turning it clockwise or anticlockwise until the cross-hairs appear distinct and sharp. 6. Focussing the thing Glass:this is often done to bring a pointy image of the thing or target within the plane of cross-hairs and to eliminate parallax. to try to to this, the telescope is directed towards object or target and therefore the focussing screw is turned clockwise or anticlockwise until the image appears clear and sharp and there's no relative movement between the image and cross-hairs. The absence of relative movement are often verified by moving the attention up and down. 7. Setting the Vernier: The vernier A is about to 0° and vernier B to 180°. to try to to this, the lower clamp is fixed. The upper clamp is loosened and therefore the upper plate turned until the arrow of vernier A approximately coincides with zero (i.e. the 360° mark) which of vernier B approximately coincides with the 180° mark. Then the upper clamp is tightened, and by turning the upper tangent screw, the arrows are delivered to an edge of tangible coincidence.
This completes the temporary adjustment required for taking readings with the theodolite.
