Slide rule
The slide rule, also known colloquially as a slipstick, is a mechanical analog computer, used primarily for multiplication and division, and also for functions such as roots, logarithms and trigonometry. It is not normally used for addition or subtraction (compare with some abaci designs, where operations more complex than addition and subtraction were not always possible).
William Oughtred and others developed the slide rule based on the emerging work on logarithms by John Napier. Before the advent of the pocket calculator, it was the most commonly used calculation tool in science and engineering, and use continued to grow through the 1950s despite analog and later digital computation devices being introduced. It was ultimately replaced by the electronic computer in the 1970s.
Relation to Computing:
The development of logarithms in the 17th century by mathematicians such as John Napier, based on work by Michael Stiffel in the mid16th century, enabled multiplication and division of arbitrary numbers to be accomplished more quickly than before, operations which were incorporated in slide rules. The sophistication of slide rules continued to be developed into the 19th century, where log log slide rules, compounding the logarithmic principal, enabled swift calculation of roots and exponents.

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Read more about Slide rule on Wikipedia.