Measurement of vertical angle, Measurement of vertical angle by theodolite practical, how to find measurment of vertical angle

• The vertical angle is one between the horizontal line ( that is line of collimation ) and the inclined line of sight.
• When it is above the horizontal line it is known as line of elevation, and when it is below the horizontal line it is called line of depression. 

    ☆ Suppose the angle of elevation angle AOC and the line of depression angle BOC are to be measured. 

1. The theodolite is setup at O. It is centered and leveled properly the zeros of ther vernier ( C&D ) marked on vertical circle, the telescope is then clamped. 
2. The plate bubble is bought to be center with ther help of foot screw, then the altitude is brought to be centered by means of clip screw. 
3. To measure the vertical angle, the telescope is raised slowly to bisect point A accurately, the readings if both vernier noted and noted the vertical angle. 
4. Ther face off instrument is changed and the point A is again bisect, the reading on the vernier are noted. 
5. Ther mean of the angle of ther observed is assumed to be correct angle of elevation. 
6. To measure the angle if depression, the telescope is lowered slowly and observation taken to be correct angle of depression.