log-log slide rule

mathematics

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June 17, 2026

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The log-log slide rule is a specialized type of slide rule that uses logarithms to perform calculations. Invented by Peter Roget in 1814, it was designed to calculate powers and roots of numbers. Unlike standard slide rules that use logarithmic scales, the log-log version has a fixed scale divided proportionally to the logarithm of the logarithm of the numbers indicated. The sliding scale is divided logarithmically.1

The concept of using logarithms to simplify calculations dates back to John Napier's discovery in 1614. This innovation transformed multiplication and division into simpler operations of addition and subtraction, paving the way for mechanical calculation aids like the slide rule. Early versions, such as Gunter's scale and Oughtred's circular and linear slide rules, emerged in the 17th century. While widely used in science and engineering, slide rules were eventually superseded by electronic calculators in the late 20th century.12

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Peter Mark Roget
…1814 he invented a “log-log” slide rule for calculating the roots and powers of numbers. From 1808 to 1840 he practiced in London. The first edition of the Thesaurus, which was begun in his 61st year and finished in his 73rd, was a product of his retirement from active medical…
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…1814 he invented a “log-log” slide rule for calculating the roots and powers of numbers. From 1808 to 1840 he practiced in London. The first edition of the Thesaurus, which was begun in his 61st year and finished in his 73rd, was a product of his retirement from active medical…
Read More

slide rule
…Roget’s Thesaurus) invented his “log-log” slide rule for calculating powers and roots of numbers. The fixed scale, instead of being divided logarithmically, is divided into lengths that are proportional to the logarithm of the logarithm of the numbers indicated on the scale; the sliding scale is divided logarithmically.
Read More
…Roget’s Thesaurus) invented his “log-log” slide rule for calculating powers and roots of numbers. The fixed scale, instead of being divided logarithmically, is divided into lengths that are proportional to the logarithm of the logarithm of the numbers indicated on the scale; the sliding scale is divided logarithmically.
Read More