Planimeter

A planimeter is a mechanical instrument used to compute the area of a planar region.

To use a planimeter, the user set up the device, zeroed the recording wheels and then traced the pointer all the way around a closed shape (typically a clockwise direction was used to produce a positive result.) The area could then be read directly off the dials. Better planimeters allowed adjustments to allow the device to read in various units and scales. Other units simply read in a fixed scale such as square centimeters and required the results to be scaled to the units required.

Donated by Akram Din.