A calculating tool, the invention of the slide rule was made possible by John Napier’s invention of logarithms, and Edmund Gunter’s invention of logarithmic scales, which slide rules are based upon.

Logarithms made it possible to perform multiplications and divisions by addition and subtraction. Look up two logs, add them together and then look for the number whose log is the sum. In 1622, William Oughtrad made the first slide rule by inscribing logarithms on wood or ivory. In 1677, Coggeshall created a two foot folding rule for timber measure, the Coggeshall Slide Rule, expanding the use of the original. In 1722, Warner introduced two- and three-decade scales.

In 1755, Everard included an inverted scale making the polyphase rule possible. In 1815, Peter Mark Roget invented the log log slide rule which included a scale displaying the logarithm of the logarithm. In 1821, Nathaniel Bowditch added trigonometric functions on the fixed part and a line of log-sines and log-tans on the slider used to solve navigation problems.

In 1845, Paul Cameron introduced the nautical slide rule including right ascension and declination of the Sun and principal stars. In 1859, French artillery lieutenant Amédée Mannheim made improvement to the four basic scales, A B C and D, to be read more precisely and easier to find squares and square roots and adding the cursor so any of the scales could be easily compared across the rule face. The “Mannheim rule” became the standard through-out the slide rule era.

In 1891, Edwin Thacher introduced the cylindrical slide rule in the United States. Also in 1891 William Cox invented the duplex rule. Read an Introduction to the Slide Rule here.

The slide rule, or slipstick, is a mechanical analog computer. They were used for all the complex mathematical calculations until 1974 when electronic calculators became popular.