What´s pocket-sized, does complex math calculations and uses movements to get answers? A slide rule.

Now Purdue University is paying homage to the geeky tool of generations of scientists, engineers and mathematicians. With nearly 200 slide rules are on display, including one donated by the first man on the moon, astronaut Neil Armstrong. By the way, he is among the Purdue alumni to donate their slide rules.

The display also celebrates the 100th anniversary of Purdue´s civil engineering department.  The exhibit, on the first floor of the university's Potter Engineering Center, features slide rules made of metal, wood, bamboo, paper and plastic, ranging in length from a few inches to 7 feet, neatly arranged in a series of panels that carefully document the history of the computational devices.   The exhibit starts with Scottish mathematician John Napier, who in 1614 discovered the logarithm with which multiplication and division could be conducted using addition and subtraction. 

"There was a point in time when the slide rule was king," said James Alleman, a professor of civil engineering who began collecting the slide rules from alumni 15 years ago. "During a period of about 400 years, anything anybody built that was of any magnitude would have required a slide rule."

The end of the exhibit also marks the end of the slide rule. The last thing on display is a 1972 HP-35 calculator that made the slide rule obsolete.

Slide Rule Still Rules

James Alleman, a professor of civil engineering, said "For centuries anyone who built anything of any magnitude would have had to use a slide rule, The slide rule ruled."

"There is nothing that is so troublesome to mathematical practice, nor that doth more molest and hinder calculators, than the multiplications, divisions, square and cubical extractions of great numbers, which besides the tedious expense of time are for the most part subject to many slippery errors," Napier wrote in a book he published under the Latin title Mirifici Logarithmorum Canonis Descriptio (Description of the Marvelous Rule of Logarithms).

Six years later, English mathematician Edmund Gunter created a number line in which the positions of numbers were proportional to Napier´s logarithms, and in 1632 fellow countryman William Oughtred used Gunter´s approach and invented the first slide rule.

But, as slide rule collector Eric Marcotte points out on his dizzyingly thorough website, it took a considerable length of time to get from these early prototypes to the modern slide rule, which can be traced back most directly to Amédée Mannheim, who developed the basic 10-inch design and scale arrangement in 1850.

Alleman said he began collecting slide rules out of personal interest and for a display to coincide with civil engineering´s centennial celebration in 1987. He ruefully admits his own first slide rule isn´t in the collection.

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