Used to determine the average effective pressure from the indicator diagram of the engine indicator easily and accurately. Also capable of, similarly to ordinary planimeters, measuring the area of intricate plane figures. Clip the figure to be measured on the plate to move the stylus along the closed figure. The difference between readings on the graduated ring before and after the stylus trip will provide the movement area of the figure in cm2. Range of the stylus: within 65 x 130 mm, One graduation on the ring: 1 cm2, Accurate reading: up to 0.1 cm2