The temporary adjustments have to be carried out at every set-up of instrument before taking observations with the theodolite.
1) Setting up the theodolite:
Setting up of the theodolite includes:
a) Centering it over the station:
Procedure:
1) Place the tripod over the stations by spreading its legs at a convenient height.
2) Suspend the plumb bob over the station and bring it exactly over the station point by moving it radially as well as circumferentially, then press the legs firmly into the ground.
3) By this the instrument is approximately levelled also.
b) Levelling up:
Accurate levelling is done with reference to the plate level by means of footscrews. The object of levelling is to make the vertical axis truly vertical.
Procedure:
1) Turn the theodolite until the plate bubble is parallel to any one of the pair of footscrews.
2) Turn the theodolite about its centre of its run by turning both, foots crews uniformly.
By thumb and forefingers either moves it towards each other or away from each other.
3) Turn the theodolite until the bubble is perpendicular to the previous position. Now, move the third footscrew until the bubble is brought to the centre of the run.
4) Repeat the process for the other two pairs.
5) Now rotate the theodolite about the vertical axis through 360°. The bubble will remain central provided it is in correct adjustment. The vertical axis is made thus truly vertical.
2) Focussing the eye piece :
Focussing the eye-piece makes the cross hairs on the diaphragm distinct and clear. To do this, direct the telescope towards the sky or hold a sheet of white paper in front of the object glass and move the eye piece circumferentially or in or out until the cross-hairs are seen sharp and black.
3) Focussing the object glass :
Focussing the object glass is to bring the image of the object formed by the object glass exactly in the plane of the cross hair. If not accurately done there is a apparent movement of the image when the observer moves up and down. This is affect of parallax. This can be removed with sharp focusing.