a mechanical device that employs the two-dimensional equivalent of this geometric trick to determine the area enclosed by merely tracing the perimeter

a mechanical instrument used to compute the area of a planar region

a simple integrating instrument for measuring the area of a regular or irregular plane surface

an instrument for the direct measurement of the areas of irregular figures drawn to scale on plans or maps

A tool used to measure the distance around a section in order to develop accurate lines drawings.

a sheet of clear plastic covered with evenly-spaced dots that are calibrated to represent a unit of area. This tool is used to determine the area of a region from a map.

An instrument used to mechanically measure an area by tracing the perimeter on a plane surface. Typically used to estimate the size of an area from scale maps.

A planimeter is a technical drawing instrument used to measure the surface area of an arbitrary two-dimensional shape. As one point on a linkage is traced along the shape's perimeter, that linkage rolls a wheel along the drawing. The area of the shape is proportional to the number of turns through which the measuring wheel rotates when the planimeter is traced along the complete perimeter of the shape.