Wikipedia Reference Information
The slide rule (often nicknamed a "slipstick") is a mechanical analog computer, consisting of at least two finely divided scales (rules), most often a fixed outer pair and a movable inner one, with a sliding window called the cursor. The slide rule was used primarily for multiplication and division, and also for "scientific" functions such as roots, logs and trig, but does not generally perform addition or subtraction.
Before the advent of the pocket calculator, it was the most commonly used calculation tool in science and engineering. The use of slide rules continued to grow through the 1950s and 1960s even as digital computing devices were being gradually introduced; but in the early 1970s the electronic scientific calculator made it largely obsolete and most suppliers exited the business.
Despite their similar appearance, a slide rule serves a purpose different from that of a standard ruler: a ruler measures physical distances and aids in drawing straight lines, while a slide rule performs mathematical operations by using distances on nonlinearly-divided scales.
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