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Difference Engines, Slipsticks to the Moon

In the early 1600s, John Napier, a Scottish mathematician who had previously developed Napier's Bones, which were multiplication tables inscribed on strips of wood or bone, invented logarithms. After the publication of Napier's work, Edmund Gunter of Oxford University developed a calculating device with a single logarithmic scale, which, with additional measuring tools, could be used to multiply and divide. In 1630, William Oughtred of Cambridge University invented a circular slide rule, and in 1632, he combined two Gunter rules, held together with both hands, to make a device that is recognizably the modern slide rule. The slide rule was to remain in common use for more than 300 years.

	Buzz Aldrin took a slide rule to the moon.

In 1815, Peter Roget (the Scotsman who gave us the thesaurus) invented the log-log slide rule, which included a scale displaying the logarithm of the logarithm. This allowed the user to directly perform calculations involving roots and exponents. This was especially useful for fractional powers. In 1859, a French army lieutenant named Amedee Mannheim developed a slide rule that was then manufactured by a firm of national reputation, which led to its being adopted by the French Artillery.

In 19th century Germany, one observatory used a steel slide rule about 2 meters long. Since astronomical work required fine computations, it had a microscope attached, giving it accuracy to six decimal places.

Throughout the 1950s and 1960s, the slide rule was the symbol of the engineer's profession. Pickett brand slide rules were the standard in the Apollo space program; a Pickett N600-MES (6 inches long, with a magnifying cursor and in "Eye-Saver" yellow) was standard equipment on all Apollo flights. Slide rules not only made getting to the moon possible, they went along for the ride.

As useful and ubiquitous as they had been, slide rules quickly passed from use with the rise of portable electronic calculators in the late 1960s.

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