Procedure to use Line Ranger Hold the line ranger in hand at the level of the eye and stand at M very near the line AB, as judged by eye. Observe the ranging rod at A through the upper prism abc. The ray of light from A enters the upper prism, gets reflected from the silvered diagonal as and enters the eye at right angles to the line AB, as the incident ray makes an angle of 45° with the reflecting surface. Also observe the ranging rod at B through the lower prism dbc. The ray of right from B enters the lower prism, goes reflected from the silvered diagonal db and enters the eye at right angles to the line AB. If the point at which the line ranger is held is not exactly on the line AB, the two images appear separated. Move the instrument slightly backwards or forwards, at right angles to the line AB until the two images appear exactly one over the other. Check whether the images of the ranging rods at A and B are seen in one vertical line or not. Transfer the point to the ground by hanging a plumb bob from the hook on the handle.
