Numbers aligned with the marks give the approximate value of the product, quotient, or other calculated result. In general, mathematical calculations are performed by aligning a mark on the sliding central strip with a mark on one of the fixed strips, and then observing the relative positions of other marks on the strips. Thus single-decade scales C and D range from 1 to 10 across the entire length of the slide rule, while double-decade scales A and B range from 1 to 100 over the length of the slide rule. Scales may be grouped in decades, which are numbers ranging from 1 to 10 (i.e. More elaborate slide rules can perform other calculations, such as square roots, exponentials, logarithms, and trigonometric functions. These common operations can be time-consuming and error-prone when done on paper. In its most basic form, the slide rule uses two logarithmic scales to perform rapid multiplication and division of numbers. The introduction of the handheld electronic scientific calculator circa 1974 made slide rules largely obsolete, and most suppliers departed the business. The slide rule's ease of use, ready availability, and low cost caused its use to continue to grow through the 1950s and 1960s, even as electronic computers were being gradually introduced. Before the advent of the scientific pocket calculator, it was the most commonly used calculation tool in science and engineering. As the rulers each have a logarithmic scale, it is possible to align them to read the sum of the numbers' logarithms, and hence calculate the product of the two numbers.Įnglish mathematician and clergyman Reverend William Oughtred and others developed the slide rule in the 17th century based on the emerging work on logarithms by John Napier.
Though similar in name and appearance to a standard ruler, the slide rule is not meant to be used for measuring length or drawing straight lines.Īt its simplest, each number to be multiplied is represented by a length on a pair of parallel rulers that can slide past each other. The slide rule is closely related to nomograms used for application-specific computations. Slide rules manufactured for specialized fields such as aviation or finance typically feature additional scales that aid in specialized calculations particular to those fields. Slide rules exist in a diverse range of styles and generally appear in a linear, circular or cylindrical form, with slide rule scales inscribed with standardized graduated markings. Maximum accuracy for standard linear slide rules is about three decimal significant digits, while scientific notation is used to keep track of the order of magnitude of results.
It is not typically designed for addition or subtraction, which is usually performed using other methods, like using an abacus. The slide rule (also known colloquially in the United States as a slipstick ) is a mechanical analog computer which is used primarily for multiplication and division and for functions such as exponents, roots, logarithms, and trigonometry. A typical ten-inch (25 cm) student slide rule (Pickett N902-T simplex trig)
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