Booking and Reducing the Levels

The booking of readings and reducing the levels may be performed systematically in the tabular form. There are two such methods:

(i) Plane of collimation method          (ii) Rise and fall method.

By the both methods for the above problem, with intermediate sights to E1 = 0.80 m and E2 = 0.70 m is illustrated below.

               Booking and reducing levels by plane of collimation method

In this method note down the following:

1. for first setting Plane of collimation

              = RL of BM + BS 2. Subtract IS from plane of collimation to obtain RL of intermediate station and subtract FS from plane of collimation to obtain RL of change point.

3. Add back sight to RL of change point to obtain new plane of collimation.

4. Check: Σ BS - Σ FS = RL of Last point - RL of first point. If it is -ve, it is fall and if +ve it is rise.

                   Booking and reducing level by rise and fall method

Note the following:

1. From A to E1, difference = 1.35 - 0.80 = 0.55, rise

2. From E1 to CP1, difference = 0.80 - 1.65 = - 0.85, fall

3. From CP1 to E2, difference = 1.40 - 0.70 = 0.70, rise

4. From E2 to CP2, difference = 0.70 - 1.70 = -1.00, fall

5. From CP2 to B, difference = 1.30 - 1.85 = - 0.55, fall.