Definition – Theodolite in which telescope can be resolved through a complete revolution about it horizontal axis in a vertical plane is known as transit theodolite.

$\underline{\text{Temporary adjustment of transit theodolite-}}$

1. Setting up the theodolite over a station

Setting up a theodolite includes following process

a) Centering the instrument over a station Point –

Place the instrument over the station by spreading the leg of the tripod well apart at a convenient height.

Plumb bob is suspended from hook approximately over the station mark.

By moving each leg radially as well as circumference, bring the plumb bob exactly over the station point then press the leg firmly into the ground.

By doing this the instrument approximately levelled.

If the instrument has shifting head centering can be done rapidly.

b) Levelling the instrument approximately by the tripod stand.

After the approximately levelling by leg adjustment the accurate levelling properly done with the help of foot screw.

Accurate levelling with the help of three foot screw included the following steps

• Step1. Turn the theodolite about it vertical axis until the plate levelled is parallel to any pair of levelling screws.

• Step2. Move foot screw either both outwards or both inward simultaneously till the bubble come in the centre of it run.

• Step3. Rotate the telescope in 900 and then bring it over the third foot screw and bubble is brought in the centre of it run by operating third foot screw either clockwise or anticlockwise.

• Step4. Again bring the telescope back to its original position at it was in step two and check the centering of bubble. Again move the pair of foot screw either both outward or both inward simultaneously till the come in the centre of it run.

• Step5. Again turn the telescope through 900 over the third foot screw and check whether the bubble remains in centre or not. Repeat these operation till the bubble remain centre for both position of the telescope.

• Step6. Now turn the telescope in any position through 3600 and observed the bubble. If bubble remain in the centre for all position of the telescope then telescope is now in accurate levelling and ready for further work of levelling.

Focusing of eyepiece and object glass to eliminate the parallax.