The setting up of the plane table includes three operations viz: 1. Levelling 2. Orientation 3. Centering.

#### Operation # 1. Levelling:

Place the table over the station-point and spread out legs to make it level and at a convenient height, preferably not above the elbow.

Then oriented and centre the table approximately as explained in the following two operations and complete the final levelling. The levelling is done by means of levelling-screws or the ball and socket arrangement or simply by adjusting the legs if there is no levelling head, with reference to a circular level or a level tube placed in two positions at right angles to each other.

#### Operation # 2. Orientation:

The table is said to be oriented when it is so placed that all lines on the paper are parallel to the corresponding lines on the ground. This is necessary when more than one stations have to be occupied by the table as otherwise the board would not be kept parallel to itself at the various stations, and the effect would be similar to using a different meridian at each station.

There are two methods of orienting the table viz:

(i) By the use of a magnetic needle and

(ii) By back-sighting.

Orientation is also possible by solving two point problem and their-point problem.

(i) Orientation by the Magnetic Needle:

To orient the table at any station other than the first, place the trough compass along the line representing the meridian drawn already on the paper at the first station and then turn the table until the ends of the needle are opposite the zeros of the scale or points towards north-south direction, then clamp the table in position. This is a quick method of orientation but is unsuitable in areas affected by local attraction.

(ii) Orientation by Back-Sighting:

Suppose the table is to be set over a station B, repre­sented on the paper by a point b which has been plotted by means of a line ab drawn from a previous station A (Fig. 6.4), the orien­tation consists in bringing ba on the paper over BA on the ground.