SLIDES RULE

Mechanical Engineering, Dec 2005 by Ehrenman, Gayle

Before the calculator, before the computer, a simple tool that worked remains far from forgotten.

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At Purdue University in West Lafayette, Ind., a permanent display on the first floor of the university's Potter Engineering Center showcases pre-digital analytical marvels. In all, the display includes about 200 slide rules from Purdue alumni, including astronauts Neil Armstrong, Jerry Ross, Richard Covey, and Roy Bridges. Another Purdue alumnus, Eugene Cernan, the last man to walk on the moon, has promised to send his slide rule, as well.

The exhibit is more than just a curiosity. It is indicative of the attachment-some might say outright affection-that these and other engineers have for an old standby with a long history. The calculator and the computer may have usurped the slide rule's place in the engineer's toolbox, but that doesn't mean the old rule has been forgotten.

"If these slide rules could talk, they'd tell stories of amazing projects," said James Alleman, a Purdue professor of civil engineering who began collecting them about 15 years ago. "There was a point in time when the slide rule was king," he said. "During a period of about 400 years, anything anybody built that was of any magnitude would have required a slide rule."

The exhibit is arranged in a series of panels detailing the history of slide rules, starting with Scottish mathematician John Napier's 1614 discovery of the logarithm that made it possible to perform multiplication and division by addition and subtraction. Six years later, English mathematician Edmund Gunter devised a logarithmic ruler with a set of dividers for adding and subtracting. In 1632, countryman William Oughtred used Gunter's approach to invent the first slide rule.

The oldest slide rule in the exhibit doesn't date back quite that far, but it does hail from the mid-1800s. In addition to antique specimens, the exhibit includes slide rules made of metal, wood, bamboo, paper, and plastic, as well as two 7-foot-long rules. The oversize slide rules were used in classes to teach students how to use them, according to Purdue alumnus and retired civil engineering professor Robert Miles, who helped design the exhibit and provided the funding for it. "Taking a course to learn how to use a slide rule was mandatory at one time," he said. "And from then on, you used it for the rest of your academic career."

It's not just the folks at Purdue who think slides still rule. When SpaceShipOne made its X Prize-winning flight, it carried some special mementos, including spaceship designer Burt Rutan's 1961-vintage college slide rule, a Pickett 3-T.

That bit of news spread like wildfire through The International Slide Rule Group, an Internet-based network for collectors of slide rules and associated mechanical calculating instruments. The group discusses everything from how best to clean old slide rules to sightings of slide rules in the latest "Ben Affleck saves the planet from extinction" movie.

This group isn't the only Web-based entity devoted to the slide rule. Walter Shawlee, president of Sphere Research in Kelowna, British Columbia, maintains the Slide Rule Universe Web site (http://www.sphere.be. ca/test/sruniverse.html), which is as information-rich as it is hard on the eyes.

Slide Rule Universe, which has been in existence since 1997, offers reference material on the care, feeding, and use of slide rules, a slide rule marketplace, and even step-by-step instructions on building a slide rule from scratch.

The site was born out of Shawlee's rediscovery of his junior high and high school slide rules, both Keuffel & Esser models.

"It grew out of a nostalgic longing," he said. "I poked around on the Internet, found other collectors, and started the Web site as an exercise to document my growing obsession. Once the site was up, I got more and more requests from people who were looking for particular models, and the marketplace grew from there."

Shawlee, who was part of the team that put together The First Edition Oughtred Society Slide Rule Reference Manual, said he gets calls all the time from teachers who need slide rules to use in the classroom. They still use the slides to teach logarithms because they find that students retain more when they learn with slides than with calculators, Shawlee said.

"People are desperate to get their kids smarter," he said. "And it's these people whose desire for slide rules touches me more than the collectors who want something different, and more exotic."

Still, Shawlee admits to falling prey to the lure of the exotic himself. He owns up to having roughly 1,000 slide rules in his personal collection, and favors pocket rules, and those he terms "the unusual, and the stunning."

"A slide rule offers extraordinary technical beauty," he said. "There's hundreds of years of history in one that survives despite our best efforts. It's like selling puppies: Someone puts one in your hands, and you have to have it."