ANS:D - planimeter

Planimeter/platometer--> measure areas in 2d.
Pentagraph-->enlarging or reducing plans.
Sextant--> horizontal angular measurements.
Clinometer/inclinometer--> angles of slope i.e. elevation or depression.
Optical Square--> laying off perpendiculars in chain surveying. An inclinometer or clinometer is an instrument used for measuring angles of slope, elevation, or depression of an object with respect to gravity. The planimeter is a mechanical device for measuring areas in the plane. It has the shape of a ruler with two legs.
The intersection is unique if the angle between the two planimeter legs is smaller than 180 degrees. The measurement consists of dragging (x, y) along the boundary of the region R. The given answer according to question is wrong. Pentagraph is the right answer.
Planimeter is used for angle measurement.
Pentagraph is used for map measurement.