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Slide Rules

Fuller's slide rule

A bracket could hold this rule at an angle for convenient operation.

Slide Rules

The principle behind a slide rule is straightforward. Two bars, each marked with scales, slide next to each other. Aligning numbers on different kinds of scales allows different calculations, such as multiplication or trigonometry. Accuracy, however, is limited and depends on the user’s skill.

Invented in the 1600s, slide rules were widely used through the 20th century.

William Oughtred

Oughtred is widely credited with inventing the slide rule in the 1620s. His initial design was for a circular slide rule, but the principles are the same.

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AEG Office, Berlin

European engineers embraced slide rules before Americans did. By 1940, however, this scene was typical of engineering offices worldwide.

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Gunter's line of numbers

This rule has Gunter's line of numbers and navigational scales on opposite sides.

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Boucher's Calculator

This is an early version of a watch-size rule. In a 1911 catalog of “Drawing Materials and Surveying Instruments” it was listed for $8 with cardboard dials, and for $14 with metal dials.

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Mannheim slide rule

Mannheim added the modern cursor to the slide rule about 1850. This early example has lost its cursor.

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Lord's Calculator

The circular scales moved independently and there was no cursor.

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Calculigraphe

Watch-size rules were popular, and even stylish, in some circles.

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Duplex slide rule

An early example of slide rules used by generations of engineers, with a sliding metal "indicator." Glass indicators were more popular after about 1910.

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Calculimetre

This is a very simple portable slide rule. The forked pointer is fixed to the brass ring with rivets and rotates with it.

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Thatcher's Rule

A rule specially designed with very long scales for greater accuracy.

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Log-Log Duplex Trig slide rule

Structural engineers often used extra-long rules for greater accuracy.

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Fowler's "Jubilee Magnum," slide rule

The 79-inch spiral scale is much more accurate than a standard 10-inch rule.

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Circular slide rule

Circular slide rules eliminated the “off the end” problem because the scales wrapped around continuously.

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Teaching slide rule

This very large teaching rule matched Pickett’s popular 34-scale Model N4-ES. Learning to use all the scales took quite a while.

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Otis King cylindrical slide rule

This 60-inch rule could be closed and slipped in a pocket. The “Model K” had just two scales and could only multiply and divide.

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Advertisement comparing slide rules to electronics

The IBM Card-Programmed Electronic Calculator, introduced in 1949, was a primitive computer created by connecting other IBM products.

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Women's Auxiliary Air Force (WAAF) officer using a slide rule

This British officer works with a Pilot Balloon slide rule to calculate upper-atmosphere wind speeds.

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Leadbetter slide rule

This four-sided rule for revenue calculations had room for more scales.

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Elizur Wright Arithmeter, No. 11

Designed by “The Father of Life Insurance” to make accurate insurance calculations.

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Lord's Calculator

This desktop calculator had very long easy-to-read scales.

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Gauger's slide rule

An unusual rule with two slides. A “gauger” was a British collector of excise taxes, particularly for liquor casks, whose volume had to be computed.

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Fowler's Textile Calculator

A specialized rule for the fabric trade, made like a large pocket watch.

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Fowler's Universal slide rule

Fowler added unit conversion markings to high-accuracy conventional scales.

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Coggeshall slide rule

A carpenter's measuring rule with a slide rule in one arm.

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Metal slide rule

A rule for calculating surveying angles and distances. Slide rules have been made from wood, steel, aluminum, bamboo, and plastic.

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The Binary Slide Rule, circular slide rule

This machinist’s rule includes rational and decimal fractions, such as ¾ and 0.75.

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Loga measurement-conversion slide rule

This rule was designed specifically to simplify conversions between different units of measurement.

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Slide rule tie clip

A popular retirement gift for engineers in the mid-1900s.

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Slide rule

This aeronautical engineering rule was made for North American Aviation.

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Log Log slide rule

Pickett was proud of their rules’ color. Their advertising claimed “EYE-SAVER Yellow prevents headaches and tired eyes; aids accuracy.”

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Slide rule

Ricoh was founded in 1936 as “Riken Sensitized Paper” and is better known now as a manufacturer of copiers and cameras.

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