Allegheny Circular Rule

This circular rule was manufactured by Allegheny Plastics Inc. since 1950, and no information of when the production was terminated. 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 equal size 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. The back face of this rule is blank, but there are (later?) versions with a fraction-decimal conversion table printed on. This rule was well suited not only for basic arithmetic operations but also for squares and square roots, cubes and cube roots. No trigonometry here.

Allegheny Plastics produced a good variety of slide rules: Aviation, Industrial, Military, Unit Conversion, among others. No serial number on this rule so it is not possible to determine the exact fabrication year, the instructions sheet has printed Copyright 1948, so it can be assumed that this rule was manufactured in the early 1950's