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Vintage “Instructions for Use of the Spirule” engineering instruction sheets.
These instructions explain the use of the Spirule for root-locus plots and control-system calculations, including vector angles, poles and zeros, multiplication of lengths and use of the Spirule’s rotating disk and arm.
The Spirule was a specialized pre-computer engineering calculating and plotting device associated with Walter R. Evans and his influential Root Locus method of control-system analysis.
Illustrated throughout with mathematical equations, root-locus diagrams and diagrams showing operation of the Spirule.
An unusual piece of mid-20th-century electrical/control engineering history with appeal to collectors of vintage calculating instruments, slide rules, aerospace engineering, electronics and early control-system technology.
Exact printing/date of this particular instruction set has not been established from the pages shown.
Includes the instruction sheets shown in the photographs. Please review all photos for exact contents and completeness.
