Allegheny Circular Rule with Protractor

This circular rule was manufactured by Allegheny Plastics Inc. during the 1950's-1960's, and there is no information of when the production finished. Allegheny Plastics Inc., formerly Permochart Company, began manufacturing precision eye charts and navigational plotters. In the the 1950's expanded its services offering offset lithograph printing on plastic, screen printing, hot foil stamping, hydraulic lamination, forming along with die-cutting, punching, shearing, profiling, drilling and assembly, being then able to produce charts, diagrams, dials, identification tags, instruction cards, signs, and slide rules. At present this company is still in business as Allegheny Printed Plastics.

This 4.25 inches circular rule was fabricated with two different sized disks, one in white plastic with scales K, D, A and L printed on, and the other in clear plastic with the scales C, B and CI, both disk screwed at their centers with a movable clear plastic indicator. This is one of the few rules I have seen with alternating movable scales. i.e. when you move the front disk you see moving every other scale. It seems that this was the Allegheny standard scale configuration for circular rules, as it can be seen in the other one in this collection, or in other collections specimens, but there is a little difference, the back face in this new model is not blank, it has printed a 360 degrees standard protractor, a fraction inches-decimal conversion table, and a Fahrenheit-Centigrade degrees conversion table. These prints on the back face make me think that this was a "basic scholar slide rule", well suited not only for basic arithmetic operations but also for squares and square roots, cubes and cube roots. No trigonometry scales were included.

Allegheny Plastics produced a good variety of slide rules: Aviation, Industrial, Military, Unit Conversion, among others. There is no serial number on this rule or any other text referring its exact fabrication year, the instructions sheet included has printed "Copyright 1948", so it can be assumed that this rule was manufactured after that year . This rule does not have the Allegheny Plastics brand label either, as the other rule in this collection, so it is assumed that this rule was manufactured by Allegheny Plastics because of the instructions sheet coming with the rule.