In this problem, two well-defined points whose position has already been plotted on the plan are selected. Then by perfectly bisecting this point a new station establish at the required position.

Procedure-

• Suppose P and Q are two well-defined points whose position are plotted on the map as P and Q. it is required to locate a new station at A by perfectly bisecting P and Q.

• An auxiliary station B is selected at a suitable position. The table is set up at B. and levelled and oriented by eye estimate. It is then clamped

• With the alidade touching p and q. the point P and Q bisect and rays are drawn. Suppose this ray intersect at b.

• With the alidade centre on b, the ranging rod at A is bisected and ray is drawn. Then the eye estimation the point a1 is marked on this ray.

• The table is shifted and centre on A with a1 just over A. it is levelled and oriented by Backsight. With the alidade touching P, the point P is bisected and ray is drawn. Suppose this ray intersect a line ba1 and a1 as was assumed previously.

• With the alidade centre on a1, the point q is bisected and ray is drawn. Suppose this ray intersects the ray PQ at a point q1 the triangle pqq1 is known as the triangle of error and it is eliminated.

• The alidade is placed along the line pq1 and a ranging rod R is fixed at some distance from the table. Then the alidade is placed along a line PQ and table is turned to bisect R. At this position the table is said to be perfectly oriented.

• Finally with the alidade centre on p and q the point P and Q are bisected and ray are draw. Suppose this ray intersects at point a. this would represent the exact position of the required station A. then the station A is marked on the ground.