Amsler's integrator; in case with rail.

Invented by Swiss mathematician Jakob Amsler in 1856, this instrument can measure larger areas than a polar planimeter, the most famous and commercially successful of Amsler’s inventions that can also measure an area on a surface. This integrator is carried by a pair of wheels moving in a straight groove in a long steel bar and a counterbalance weight is provided. When the pointer is guided to completely describe the outline of a plane figure, the graduated roller attached to the swinging art registers the area of the figure.