Notes: "This polar planimeter was made by A. Ott in Germany for Dietzgen. It features an adjustable length tracing arm so that the planimeter can be adjusted to read directly in the units of the chart being measured. An unusual feature of this planimeter is the rectangular pole arm weight, which stays in place by friction with the paper underneath, not by sticking a sharp point into the drawing. There is no model number either on the planimeter or on the calibration chart in the box."
