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Aristo Slide Rule
Educational tool for alphabet substitution

One of the most elementary hand cipher tools for learning the basics of cryptography is the blank Aristo 90197 slide rule. It was used for training new cryptanalists with the principles of alphabet substitution, shifting and transposition, and is in fact the blank variant of a standard slide ruler.

A slide rule, in the US also known as a slipstick, is a mechanical analog computer 1 that was used for scientific calculations like multiplication, division, roots, logarithms and trigoniometry. Invented in 1622 by Reverend William Oughtred in the UK, it was the most popular calculation device in science and education before the arrival of the pocket calculator around 1974 [1].

Over time, a wide variety of specialized slide rules were developed for specific fields like navigation, engineering, antenna calculations, proof calculations, education, photography, etc.
  
The Aristo slide ruler taken out of its box

Although the name may suggest otherwise, a slide rule was not used for taking measurements. The most basic design consists of two fixed parts, with a sliding section in the middle. By using a blank variant of the slide rule, with evenly spaced cells, it becomes a useful practicing tool for simple alphabet substitutions and transpositions; two of the basic operations in cryptography.

The image above shows a typical blank slide rule made by Aristo in Germany, one of the major manufacturers of educational tools in Europe. The slide rule is made of plastic and is printed with vertical bars only, allowing letters to be written inside the individual cells with a pencil. Because of its simplicity it could be used for nearly every language. It was used for the education of cryptanalists in Europe throughout the Cold War and is very similar to the Dutch Caesar Box.

  1. The word computer should not be confused with a modern automatic programmable digital computer. Please note that a computer was initially a person that performed calculations (calculator) and that the name was later also used for automated calculations, both mechanically and electronically [2].

Packed inside a plastic container The slide ruler unpacked from its container The Aristo slide ruler taken out of its box The blank Aristo Slide Ruler One end of the slide ruler
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Packed inside a plastic container
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The slide ruler unpacked from its container
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The Aristo slide ruler taken out of its box
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The blank Aristo Slide Ruler
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One end of the slide ruler

References
  1. Wikipedia, Slide rule
    Retrieved August 2015.

  2. Wikipedia, Computer
    Retrieved August 2015.
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Crypto Museum. Created: Thursday 12 August 2010. Last changed: Wednesday, 05 July 2017 - 20:24 CET.
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