Todd Tolhurst

I collect slide rules. For those of you who don't remember a time before inexpensive electronic calculators, slide rules are simple but devilishly clever calculating devices. Capable of performing many types of computations, including multiplication, division, logs, antilogs, powers, roots and trigonometric functions, slide rules were once the constant companion of working engineers and scientists.

Around 1973, Hewlett-Packard introduced a revolutionary product, the HP-35 electronic slide rule calculator. For the first time, a small electronic device was capable of doing all of the computations done by slide rules, and then some. Although the HP-35 was rather expensive (around $400, which might be a week's pay for a young engineer), it was only a matter of time before the price of calculators dropped to the point that slide rules were no longer competitive.

My Collection

Here is a list of the slide rules currently in my collection. I have only begun to scan them, and I'll be adding more pictures Real Soon Now.

Concise (Sama & Etani)
Sama & Etani seem to have specialized in circular slide rules, usually sold under the Concise brand. Many of these rules were made for companies who used them as promotional giveaways, and so they were often imprinted with company names, logos and slogans.  • Concise CTCS-552
 • Concise (SIC) 300B
Dietzgen, like many other makers of drafting and engineering instruments, also marketed a line of slide rules. Although not quite as common as rules from K&E, Post or Pickett (at least in the U.S.), Dietzgen's rules were of the highest quality.  • Dietzgen 1734
 • Dietzgen 1738
One of the major European slide rule makers, Faber-Castell offered a wide variety of rules in wood and plastic, including the unusual addiator rules with combined a slide rule with a mechanical adding machine.  • Faber-Castell 67/87
All the Gilson rules I've seen are variations on the same design -- circular solid aluminum rules of the dual-cursor type. Many of these rules included scales for fractional equivalents, screw sizes and thread pitches, presumably suiting them for use in mechanical trades.  • Gilson Binary
As the manufacturer of most of the Post rules, Hemmi is the most familiar Asian slide rule maker to those of us in the U.S. Hemmi also sold rules under its own name and others (Hughes-Owens in Canada, for instance). Although the firm also made quality plastic rules, Hemmi is best known for its bamboo-core rules.  • Hemmi 149A
 • Hemmi 153
 • Hemmi 257 Chemical Engineering Rule
Keuffel & Esser
K&E, the late great maker of drafting and engineering instruments, was probably the brand name most synonymous with "slide rule" for generations of American engineers. K&E's wooden rules were made of celluloid-laminated mahogany. Plastic (Xylonite & Ivorite) rules were also made.  • Keuffel & Esser 4080-5
 • Keuffel & Esser 4081-3 (2 of these)
 • Keuffel & Esser 4161-1
 • Keuffel & Esser 68-1100 Decilon
 • Keuffel & Esser 68-1210
Otis King
The Otis King Calculators are long-scale slide rules in which the scale has been wrapped in a spiral around a cylinder. These clever British rules pack a 66-inch scale into a package not much longer than a pocket slide rule.  • Otis King Model K
Pickett rules are distinctive for their metal construction, as opposed to the traditional wood or bamboo cores used by most other makers. Pickett capitalized on the "hi-tech" feel of its aluminum-body rules (some early models were magnesium) through heavy marketing to schools and students. Although Pickett rules lack the finesse of other top brands (in my humble opinion, of course), they did produce some rules of considerable sophistication and complexity. Pickett also made a number of inexpensive plastic rules (which were still way nicer than Sterling rules), and even one model executed in bamboo.  • Pickett 140
 • Pickett N3-T
 • Pickett N500-ES
 • Pickett N600-T (2 of these)
 • Pickett N902-T
Frederick Post Co. (later, Teledyne Post) slide rules were by and large made by Hemmi, except during World War II, for obvious reasons. Like all Hemmi rules, these were of very high quality, constructed of a bamboo core overlaid with plastic scales. Post also sold some all-plastic rules as well.  • Post 1447
 • Post Versalog II 1460 (2 of these)
 • Post Pocket Versalog 1461
Scientific Instruments Co. (SIC)
SIC appears to have been a brand name under which number of different rules made by various manufacturers were marketed; the Concise 300B listed under Concise also bears the SIC brand. Both of the SIC circular rules I own are of very good quality.  • SIC 1610
Without a doubt, Sterling Plastics made some of the world's very worst slide rules. All-plastic construction, with sticky slides, misaligned cursors and smudgy scales, Sterling rules were nonetheless fascinating to me as a kid. Since they sold for about a buck or two at the five-and-dime, they were within my budget, too.  • Sterling Mannheim Trig #689
 • Sterling Decimal Trig Log-Log


Other Calculating Instruments

Here's a few other calculating instruments in my collection:
   • Dalton-Weems E6B Flight Computer
   • Tasco Pocket Arithmometer

Slide Rule Links

Slide Rule Universe
Sells used & mint-in-box slide rules. Great source of information.
Dave's House of Slide Rules
This guy cracks me up. A wonderful collection of rules, and a lot of good information.
Kung's Slide Rule Collection
Some good links to other slide rule-related web pages
Liam's Slide Rules
A very nicely-done slide rule site by a fellow amateur radio operator