The once-mighty slide rule makes a comeback (among scholars and collectors)

slide roto rule

A circular “RotoRule,” which was developed in the early 1930s, boasted two spiral scales with the accuracy of a 50-inch slide rule.

It's the kind of memory that could almost bring tears to the eyes of a collector. In the mid-1970s, just a few years after the introduction of Hewlett-Packard's first electronic pocket calculator, petroleum engineer Tom Wyman stood in the Stanford Bookstore gazing at a generously stocked display of slide rules, all offered for sale at a fraction of their original prices.

Wyman considered buying a 20-inch-long rule, which he'd previously considered a splurge, he said. But by then, he had traded in his slide rules for an electronic calculator. Looking back, "I should have bought them all," said Wyman, now president of the Oughtred Society, a group dedicated to the history and preservation of the slide rule and other mechanical calculators. Wyman also is one of two curators of the exhibition The Rise and Fall of the Slide Rule: 350 Years of Mathematical Calculators in the Peterson Gallery on the second floor of the Bing Wing in Green Library.

The exhibit, which traces the history of the slide rule and its applications, is drawn from the personal collections of Wyman, a Stanford alumnus and associate of the Stanford University Libraries, and Robert K. Otnes, an engineer specializing in communication theory, both of Palo Alto. The exhibit, on display through Oct. 9, is free and open to the public.

Scottish theologian John Napier laid the foundation for the invention of the slide rule in 1614 with the invention of logarithms. In 1622, the mathematician William Oughtred set two straight edges marked with logarithmic scales side by side and created the first rectilinear slide rule.

For the next 350 years, the slide rule, well, ruled. Indispensable to anyone who routinely made mathematical computations, they were "the most convenient calculating instrument available," Wyman pointed out. The electronic calculators that came into use in the 1960s and 1970s so completely eclipsed slide rules, however, that the once ubiquitous tool began to slide toward obscurity. ("Oh, you've got one of those wooden calculating sticks," a young MBA once exclaimed at the sight of a slide rule in Wyman's office.)

In recent years, enthusiasts like Wyman and Otnes have made slide rules highly sought-after as collectibles. The dozens of antique and modern slide rules in the Green Library exhibit—which range from a blocky 17th-century boxwood slide rule manufactured in 1693 to modern plastic rules designed to tuck into a shirt pocket—are "just the tip of the iceberg" of his and Otnes' collections, Wyman said.

Although the craftsmanship of some slide rules—such as a German silver and ivory rule made in London circa 1860—approach fine art, much of the satisfaction of collecting comes from piecing together the history of the slide rule's development, Wyman said. It demands a detective's skill, since thousands of different slide rules were created but many of them have survived without the instruction booklets that accompanied them, he said. Until recently, there were only one or two sources on the slide rule's history, Wyman added.

Wyman has written his own history of the slide rule and numerous other articles, which have been published in the semiannual Journal of the Oughtred Society. (Otnes, also a prolific writer on the subject of slide rules, is the journal's editor.) "There are lots of articles yet to be written, " Wyman said. "You go on the hunt and then feel obligated to share what you find with others."

A particular gift of the two engineer-curators is in bringing to life the evolution of applications for slide rules, beginning with the display of artifacts used by 18th-century British excise officers, who carried slide rules for calculating taxes on casks and barrels of alcoholic beverages. The slide rule developed along with the Industrial Revolution and the exhibit includes a "Textile Calculator" and other slide rules used to compute weaving prices in the 19th century.

The exhibit also highlights the ingenious solutions of slide rule designers in their quest for greater precision. The longer the scale, the more accurate, but practical considerations limited the length of slide rules, Wyman said. The Fuller Calculator, which is the size and shape of a large rolling pin, had a cylindrical rule with a 500-inch scale, accurate to five decimal places. (It was available from 1895 to 1926 and was a favorite of insurance company analysts.)

In addition to the Green Library exhibit, about two dozen slide rules are included in a small display, The Engineering Slide Rule: Calculating Before Electronic Computers, in the Engineering Library at the Terman Engineering Center.

"It gives engineering students an idea how lucky they are to have calculators," said Wyman.

The exhibit cases in Green Library are illuminated Monday through Friday from 10 a.m. to 6 p.m.; on Saturdays from 10 a.m. to 5 p.m. and on Sundays from 1 to 6 p.m. The gallery is accessible whenever Green Library is open and hours vary with the academic schedule. For library hours, call 723-0931.

The Engineering Library is closed on Saturday and Sunday. Hours vary with the academic schedule. For information, call 723-0001.

slide stanley