Savor your slide rule

This long-time symbol of engineering has retained its value, says Editor in Chief Mark Rosenzweig in his monthly column.

By Mark Rosenzweig

In one of my desk drawers are two slide rules that I got while in engineering school — a K+E “log log duplex vector” and a Dietzgen “decimal trig type log log.” Both sport 22 finely engraved scales for handling multiplication and division, proportions, squares and square roots, cubes and cube roots, plane trigonometry, exponents and logarithms. I have always had a fondness for the two, appreciating their ivory-like-plastic-over-wood construction, smoothly moving cursors and genuine leather cases. I still remember arguing in college over the merits of the K+E and Dietzgen versus their all-metal rival from Pickett.

True, computers have largely supplanted slide rules. But don’t scoff at slipsticks. A 50-year-old Dietzgen may well be worth more than a 3-year-old Dell.

Some antique slide rules fetch $2,500 or more, according to Walter Shawlee, who runs Sphere Research Corp. in Kelowna, B.C., which hosts the Slide Rule Universe Web site ( These though, he notes, are mechanical oddities, like the cylindrical K+E Thacher (, which were uncommon and are very complex.

The traditional slide rules that many engineers viewed as symbols of our profession haven’t been made for decades, says Shawlee. The advent of pocket calculators caused their demise. By 1973, production had been halted by major makers. However, substantial quantities of unsold slipsticks remained. Indeed, such “new old stock” slide rules still are available. Sphere Research, which is one of several firms that sells them, now offers more than two dozen types of vintage-but-new slide rules ranging in price from $39 for a Pickett “simplex trig” to $175 for a Hemmi/Sun “mechanical engineering duplex.” Besides these makes, Sphere currently sells slipsticks from producers such as Germany’s Aristo, Faber-Castell, Nestler and Staedtler-Mars, Japan’s Fuji and India’s Deeva. Quantities range from a single piece to a couple of hundred.

While unused slide rules might continue to be unearthed — Shawlee cites one collector, Foo in Singapore, who relatively recently found a stash of about 3,500 rules, still new in their crates, that had remained untouched for 30 years — available new old stock is shrinking rapidly, he says.

Shawlee sold about 2,500 slide rules in 2005, which he considers a reasonably good year. He reckons that about 75% of his customers actually use their slide rules, while 25% buy them for their collectible value but will play with them occasionally.

Slide rules boast one powerful advantage over calculators, says Shawlee: once a particular ratio is set up, all possible answers are shown. It takes endless serial calculations to equal that feature, he notes.
Interest started picking up about five years ago, following some media coverage, and remains strong, he says. There are several collectors groups, including the Oughtred Society (, which was founded in 1991 and now has members in 22 countries. Mike Konshak runs an on-line museum (, which showcases “well-used calculators for hairy-eared engineers.” Sphere Research provides more than a dozen slide-rule links on its Web site.

Meanwhile, cardboard slide rules designed for specific calculations — the ones frequently offered gratis by vendors of equipment — still are produced in the millions each year by a number of companies. “In fact,  more are made annually than were made in total during the life of traditional American slide rules,” says Shawlee.

It’s reassuring that this symbol of our profession is not sliding into oblivion.