Related Object Info
compensating polar planimeter
The planimeter is stored in a black rectangular case that opens with two hinges along a long edge. There are two metal clips on the lid of the case that snap onto two metal pins attached to plates on the front of the bottom half of the case. The inside of the case is lined with blue velvet. The bottom half of the case is contoured to fit the pieces of the instrument. There is a white card inside the case with instrument and conversion information.
The planimeter breaks down into three main pieces. The longest piece is a black, rectangular metal bar that sits on top of a large brass puck at one end and a silver metal pin at the other end. Secondly, there is a shorter, flat metal tape with a small hole at one end.
The third main piece consists of a shorter black, rectangular metal bar, called the tracer arm. There is a metal roller whose axis is perpendicular to the shorter black bar at one of its ends. Also at that end, there are two short, black rectangular bar offshoots, each perpendicular to the main bar. At the place where each of these arms branches from the main bar, there is a hole part way through the top of the main bar. These two bars serve to frame and support two measuring devices. One device consists of a flat white disc with incremental measurements from 0 to 9 marked around the circumference. The disc lies flat on top of the black metal bar. There is a black arrow that is attached to the black bar and one end and the other end lies flat on the disc pointing to the measurements. Beneath the disc, parallel to the main bar, there is a thick, silver metal screw. The second measurement device consists of a wheel and the subsection of a wheel, both white with black markings. The axis of both runs parallel to the black bar and connects with the silver metal screw beneath the white disc. The wheel is incrementally marked with the numerals from 0 to 9, and each increment is further subdivided into 10 sections. The wheel subsection has a single unit, one end marked 0 and the other marked 10 with 10 equally spaced lines between them. The wheel subsection serves to increase the accuracy of the readings made on the wheel.
At the opposite end of the smaller black bar from the measurement mechanisms, there is another, silver metal rectangular bar. The latter rests on top of the former so that they overlap for part of its length and then it extends past the black metal bar for the rest of its length. The silver metal bar has a set of etched measurements on part of the subsection that rests atop the black bar. The measurements are equally spaced, with the increment closest to the stylus marked 25 and the increment closest to the measurement mechanisms marked 33. Each increment is subdivided in ten by small lines.
Beneath the section of the black bar above which the incrementally marked silver metal bar sits, there is a silver metal screw. The screw can be loosened to permit users to adjust the placement of the silver metal bar on top of the black metal bar. In between the incrementally marked section of the silver metal bar and the black bar on which it sits there is a short metal pin that rests flat on the top surface of the black bar, directly beneath one of the measurement increments.
At the end of the metal bar that does not rest atop the black bar, there is a black metal clamp. A silver metal stylus next to a small metal stand and brass screw extend below the clamp, and a brass screw extends above it. The black clamp has a depression on either side. Users are meant to put their thumb and middle finger in the depressions and to rest their pointer finger on top of the brass screw, extending above the clamp, when directing the stylus.
When the instrument is assembled, the silver metal pin at one end of the longer black metal bar sits in one of the holes through the top of the shorter black bar. These holes are located at the two junctions from which the short black offshoots that frame the measuring devices emerge.
The Keuffel & Esser Co. Manual for compensating polar planimeters that details the design and function of the instruments can be found here. Pages 8 - 9 deal specifically with this model, the 4238.