Polar planimeter with pole arm, magnifying glass and calibration checker bar in a box. No 2838. The calibration sheet is dated December 1935..
Planimeters are used to calculate the exact area within an irregular shape. To use the planimeter, the pole arm is attached to the planimeter and then the weight is attached to the end of the pole arm to support the planimeter and to ensure it stays in one place. The pole weight is usually set outside the area to be measured.. The tracer arm on which the tracer point has been attached is used to trace clockwise around the edge of the shape to be measured. The magnifier glass when attached to the planimeter can be rotated to read either the scale setting vernier or the measuring vernier. The scales are set to 0 before use.