In a telescope the object glass of focal length 14 cm, is located at 20 cm from the diaphragm. The focussing lens is midway between them when a staff 16.50 m away is focussed. The focal length of the focussing lens, is

Surveying and leveling is a measurement process that determines the height of the level and the distance of an area with another elevated surface.

The principle of levelling is to obtain a horizontal line of sight at which the vertical distance of a point above or below this line of sight is found.

The main purpose of balancing in the survey is: Find the heights of the given points in relation to the given data.