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The ACU-Math rules were produced in the United States from 1938 until 1972 by Festus Mfg. Co., as a need after the Great Depression years of low cost slide rules. Festus Mfg. Co. was re-branded ACU-Rule in 1939 and provided also production capacity for other brand names, such as Dietzgen and Frederick Post. In 1938 Sterling Plastics bought Acu-Rule but continued using the ACU-MATH logo for their higher quality slide rules.
The Model 511, for students and other users not needing to use the Log-Log scales, was produced since 1945, and was fabricated with metal (Magnesium) covered with white vinyl and plastic cursor and hold with metallic braces. Initially branded 511 Student Mannheim, it was designed to do not reverse the rule's slider. The scales: S, K, A [ B, CI, C ] D, L, T are all on the front face, and units and fractions conversion tables on the back face. In the early 1950's the rule evolved to 511 Mannheim Professional, keeping the same scales set, but adding to the back face tables an excellent Trigonometric and Geometric Formulas table. This final formula set is so good that was included by other manufacturers in some of their Students models
By 1955 was produced the Model 600 Basic Trig, a plastic made rule, plastic cursor and also hold with metallic braces, identical to the 511 but with an additional trigonometric scale S&T for small angles.
These models are among my favorites. As HS Math teacher the formulas at the back face are really useful for teaching and math practice. I'm sure that that if I were a teacher in the 1950-1960's, I had a class set of these rules.
It is difficult to precisely estimate the year these rules were fabricated because there are no serial numbers on them. Only can be concluded that the rules in this collection were fabricated in the 1950's
A skillful student could solve the next problems using a 511 or 600 model, with a precision of two or three decimals:
SlideRulePractice-1.pdfHere is the scan made by the International Slide Rule Museum of the User Manual:
ISRM_M278_Acu-Math_44P_Inst_GiftOfMaureenWhiteForPhillipMurray.pdfClick on the next links to see professional panoramic pictures of the N-511 and N-600 models.
Click on the next links to see professional panoramic pictures of the N-511 and N-600 models.
511 Student Mannheim
https://www.sliderulemuseum.com/Acumath/S447_Acumath_511_StudentMannheim_EarlyMagnesium.jpg
N-511-ES Professional Mannheim
https://www.sliderulemuseum.com/Acumath/Acu-Math_511_MagnesiumPlastic_c1950_GiftOfNormaTanner.jpg
N-600-ES Basic Trig
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