The planimeter was a mechanical device that was used well before the mid-20th century. Determining the area of surfaces bounded by natural boundaries could be a challenge without it. One could divide an area into rectangles and triangles of which the area of each could be calculated and then all totaled, however that was time consuming and not very accurate. In 1818, Johann Martin Hermann, a Bavarian surveyor, built the first planimeter, a mechanical device which enabled the operator to obtain the area of a closed surface by tracing around its boundaries.
Planimeter, ALSA 2006.11.01
Planimeter, Stanley
Planimeter, Hughes Owens
Planimeter, A.OTT
