此款線性式求積儀為美國紐約John S. Bushnell公司生產，其設計為改良John Coffin於1882 年發明的求積儀。該求積儀主要用於測量蒸汽機上的儀表所繪製的曲線下的面積。

This linear planimeter, produced by John S. Bushnell of New York, USA, is an improved design of the planimeter invented by John Coffin in 1882. It is used to measure the area of irregular shapes, particularly steam engine indicator diagrams.