Slide rule

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Slide rule

The slide rule, also known colloquially as a slipstick, is a mechanical analog computer used primarily for multiplication and division, as well as for functions such as roots, logarithms, and trigonometry, but not typically for addition or subtraction. Slide rules come in a diverse range of styles and generally consist of three parts: the body, the slider, and the cursor.

History

The invention of the slide rule is attributed to the English mathematician John Napier of Merchiston, who is also credited with the discovery of logarithms, an essential mathematical tool that made the slide rule possible. The first slide rule was created in the 17th century, shortly after Napier's invention. The device underwent significant development over the centuries, with the addition of the cursor by English mathematician William Oughtred in 1632, which greatly enhanced its utility.

Throughout the 19th and early 20th centuries, the slide rule was an indispensable tool for engineers, scientists, and students. Its popularity began to wane with the advent of electronic calculators in the 1970s, leading to its obsolescence in professional settings by the end of the 20th century.

Design and Operation

A typical slide rule consists of a fixed body and a sliding central strip, with scales engraved or printed on both. The user aligns the scales using the slider to perform mathematical operations. The precision of a slide rule is limited by its physical size and the user's ability to interpolate between scale markings.

Scales

The most common scales found on a slide rule include the C and D linear scales for multiplication and division, the A and B scales for square roots, and the K scale for cube roots. Trigonometric functions, logarithmic scales, and other specialized scales may also be present, depending on the complexity of the slide rule.

Types of Slide Rules

Slide rules come in various forms, including the standard straight rule, the circular rule, and the cylindrical rule. Each type offers different advantages in terms of ease of use, precision, and portability.

Straight Slide Rule

The straight slide rule is the most common form, consisting of a linear scale along which the slider moves.

Circular Slide Rule

Circular slide rules, designed with a rotating disc, offer the advantage of a more compact form factor while providing similar functionality to the straight slide rule.

Cylindrical Slide Rule

Cylindrical slide rules, also known as helical slide rules, provide increased accuracy through longer scales wrapped around a cylinder. These were used for more precise calculations, such as in aviation and navigation.

Impact and Legacy

The slide rule was a critical tool for calculations in science and engineering before the widespread availability of electronic calculators. Its use taught generations of professionals the importance of estimation and the limitations of precision. Today, slide rules are primarily collected as historical artifacts, though they still find use in education to teach the principles of logarithms and analog computation.

See Also

• Analog computer
• Logarithm
• John Napier
• William Oughtred