Coradi Polar Compensating Planimeter Sold by Keuffel & Esser (Model 4242)

The adjustable tracer arm on this German silver and bronzed brass instrument is evenly divided to tenths of a unit, with each unit equal to 5mm, and numbered from 5 to 36. The measuring wheel, vernier, and registering dial are white plastic. A second vernier is made of German silver and used with the scale on the tracer arm. The carriage for the measuring wheel is marked: N^o 25743. The pole arm fits inside a tube attached to a cylindrical weight, allowing the arm's length to be adjusted. The pole arm has a scale like the scale on the tracer arm, but it is numbered from 30 to 34. The tube is marked: G. Coradi, Zürich Switzerland.

An oblong German silver testing rule is marked for 0", 1", 2", and 3". It is also marked: G. Coradi Zürich. A wooden case covered with black morocco leather is lined with purple velvet. A printed paper chart is pasted inside the case. The chart has columns for Scales, Position of the vernier on the tracer bar, Value of the unit of the vernier on the measuring roller, and Constant. The values in the Position and Constant columns are handwritten in the same hand that indicates the Coradi firm manufactured this planimeter with serial number 25,748 in 1917.

The label is also stamped in purple: 4242. This was the model number used by Keuffel & Esser of New York, which sold the instrument from 1901 to 1972. The price was $46.50 in 1909, $33.50 in 1915, and $55.00 in 1921; presumably, World War I affected Coradi's ability to export planimeters. By 1936, a German firm was manufacturing model 4242 for K&E's Paragon product line. Compare to 1998.0032.03. See 1991.0882.02 for a later instruction manual.

The instrument was received at the Smithsonian in 1999.

References: Clark McCoy, "Collection of Pages from K&E Catalogs for the 4242 Family of Polar Planimeters," http://www.mccoys-kecatalogs.com/PlanimeterModels/ke4242family.htm; Catalogue of Keuffel & Esser, 33rd ed. (New York, 1909), 322; Catalogue of Keuffel & Esser, 35th ed. (New York, 1915), 315; Catalogue of Keuffel & Esser, 36th ed. (New York, 1921), 257; Catalogue of Keuffel & Esser, 38th ed. (New York, 1936), 340.

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