Planimeter
The planimeter is a table-top instrument used to measure the area of a two-dimensional space on a map. It consists of two arms, one which stays fixed and one which traces a curve. As one arm moves, the measuring wheel turns, and the total distance moved is accumulated on the dial next to it. After a curve or space is completely traced with the pivot arm, the surveyor can use mathematical calculations based on the configuration of the planimeter to determine the area of the space traced.