You set the input number by sliding the center sliding part arrow, to align with a number on the static part. There are many scales along the ruler, where you can pick off the answer by reading across.
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William Oughtred and others developed the slide rule in the 17th century based on the emerging work on logarithms by John Napier.
William Ougthered invent Slide Rule in 1622!
AnswerThe slide rule was invented by William Oughtred in 1625. AnswerWe do not know the precise year. A circular slide rule was invented by William Oughtred some time about 1620, and a design of a similar slide rule by Delamain was printed in about 1630. The straight slide rule seems to have been invented later, some time around 1650.
Yes, it is a point on the slide rule. It is exact and not a decimal number.
William Oughtred (1574 - 1660) was an English mathematician and scholar. He used previous work by Napier, Gunter, and Delamain design a circular slide rule. This made approximate calculations much easier and faster than other methods of the time. The slide rule was reinvented in a sliding bar format in the 1650s. In addition to making calculations easier, the slide rule made teaching of logarithms more understandable.