Notes: "The rule form planimeter was designed to measure larger areas, or mean heights of data traces on strip charts. The planimeter has no pole arm, and instead there is a rounded peg on the underside of the frame that rides in a groove on a steel rail, much like an integrator would use. This is the large size, calibrated in inches, and the model number would be determined by the rail it originally came with (which is missing): model A2220 had a 48"" rail, A8221 a 36"", and A8222 a 24"" rail. One of the pictures is from a 1959 Stanley catalog and shows how it was used on the rail."
