Measuring average height of plots on circular charts.
Notes: "This planimeter was patented by W.F. Durand in 1909, manufactured in Switzerland by Amsler, and sold in the USA by The Industrial Instrument Co. of Foxboro, MA. William F. Durand was an interesting person. While in the Navy, Durand was loaned out to teach steam engineering, earning a PhD while teaching. He taught engineering at Cornell, Purdue, and finally Stanford. Along the way he invented this planimeter as well as logarithmic graph paper."
