The stArt of Collecting Slide Rules
My interest in vintage slide rules began in Naperville, Illinois, in about 2008. For a few months my wife and I spent time looking around antique stores in search of antique glass pieces that she had begun to collect. It did not take very long before I was addressed with the statement, “You should find something that you would like to collect,” meaning, I thought, that if I did, perhaps I would not simply tag along three feet behind her as we strolled through a vintage marketplace. But nothing I found in the stores really piqued my interest until one day when I found a 12-inch long mahogany Keuffel and Esser (K&E) slide rule sitting on a shelf in a now-defunct antique store in downtown Naperville. Though I was required to have a slide rule in my high school science classes, I was accustomed to the cheap plastic rules produced for high school students in the 1970s. My three specimens were sitting in the back of a desk drawer at work, as my first electronic calculator became available to me as a high school Senior in 1975. But I still remembered — just a bit — how to do some basic calculations. I had become familiar with the Pickett metal slide rules, as I knew someone who had one in their office at work, and I had seen students at school with Pickett’s plastic rules. But I had not paid any attention to slide rules since 1975. I was not at all familiar with the fact that fine wooden slide rules had actually been “a thing” at one time.
Needless to say, I bought the K&E (shown above; it was about $20) and I was anxious to look it up online when I got home to see what a remarkable find I must have made. But what I learned was that my new old slide rule was just a small part of a whole world, all new to me, of a huge variety of slide rule models, makers, styles, scale sets, manufacturing materials, and so on, that were feeding a whole community of collectors, historians, and enthusiasts. Most of my “hits” online were tied to a virtual museum — the International Slide Rule Museum (ISRM) — that had a picture and information about my new slide rule, and other hits referenced journal articles and a web site produced by a public group of collectors, members of the Oughtred Society. At this point I knew what I wanted to look for while on our antiques excursions.
Time went by and slide rules started to stack up. After a bit of review, I re-learned the computational techniques I learned in high school, and began to learn about the more advanced scales that were on my early rules but weren’t required to learn in school. At this time, I was able to find slide rules — sometimes two — in almost any reasonably sized antique store or mall. After about 20 or so slide rules I knew that I needed a list of what I already owned, if only to check while in a store as to whether the one in front of me is on the list or not, and so a spreadsheet was created. And soon, the spreadsheet found itself online, too, so that I could access it when on the road. It was during the shutdown during the COVID pandemic that I turned the spreadsheet into a web page.
I learned during this process that while K&E — the first major producer of slide rules in the U.S. — was started in the New York City region in the 1880s, it was Chicago that was the birthplace of many of the other major U.S. slide rule makers and distributors, such as Dietzgen, Frederick Post, and Pickett, and others. (This will be a topic of a future post for sure.) So I have been fortunate as a collector to be located within an hour’s or so drive from the U.S. epicenter. Over the past few years though, I have noticed that slide rules are much more rarely found in the antique stores these days. However, there is no shortage of them for sale online. One can find very nice basic and intermediate slide rules online at the same price or lower than my first mahogany K&E slide rule.
A search for slide rules for sale online will turn up items found on eBay, the site with the greatest number of listings. Other sources, like Etsy and Mercari, will have slide rules, but far fewer and often cross-listed with eBay. One other good source is Facebook Marketplace, where one might find a slide rule for sale in your own neighborhood. In addition, other sites, including Following the Rules and Sphere Research, have limited supplies of slide rules for purchase, and the IRSM site has slide rules that can be obtained through a donation.
For general information on the slide rule, its use, and the art of collecting, the Oughtred Society is a very good resource. Its site has reference material, beginner’s guides, a page of useful links, and a searchable archive of articles from their Journal. And in the UK — where it all began — the United Kingdom Slide Rule Circle also has its “Gazette” and links and guides online, though there is a bit of overlap with the Oughtred Society page. Both of these organizations offer memberships with modest fees that provide access for its members to further information, with meetings held most years (mostly online now) providing a chance to meet other interested parties and hear talks by the experts. And then there are sites like mine, generated by enthusiasts and collectors that just like to share what they have found and what they have learned. Both the OS and the UKSRC have links to many such web sites.
As for what to look for in a slide rule? This is very much acquired through experience. I found that I just needed to grab a few and get a feel for them, their construction, the arrangement of their scales, and of course their age. As the slide rule went out of production in the mid-1970s, samples of advanced rules from that decade are a little more scarce, partly because not as many were made, and partly because people who bought them back then may still have them! These often have the most scales and most interesting functionality. So, it turns out, slide rules from the 1940s through the 1960s appear to me to be more easily found today. Personally I like the slide rules from the early 1900s, when there was a lot of changes going on as science and technology was driving the need for high-quality slide rules. I have become drawn toward early rules, advanced rules for general calculations, and interesting specialty slide rules. While I don’t feel the need to have “one of everything”, I do like to acquire samples of rules that “fill in the gap” and help to tell the story of the slide rule’s development. And, of course, slide rules close to 200 years old or older do that and are exciting to find — and they still can be used today for calculations!
Then, there are variants in style, such as the standard “linear” rule-like slide rule versus the circular-style slide rule. It was interesting to find that the inventor of the slide rule, William Oughtred, created a circular slide rule in the early 1600s! More rare are examples of cylindrical, spiral, and helical designs that can provide greater accuracy from having longer scales on a device of manageable size.
Besides the development of the scales for doing calculations, the technologies used in slide rule manufacturing also have an interesting history that is ripe for study and the forming of collections. The quest to create reproducible, highly-accurate scales on rules that could withstand changes in temperature, humidity, and the wear and tear of the daily grind without loss of accuracy and precision led to new patents and manufacturing equipment that allow us to continue today to use and maintain slide rules that were made 100 years ago.
The best way to get into collecting slide rules is to acquire one, study its construction and its scales, and start learning how to use it. Then, perhaps using the resources provided above, begin looking for answers to the questions that you will undoubtedly pose. The quest for those answers, of course, will bring about new questions, and off you go…
Postscript: And just like that, after writing the words above that the internet is the place to find slide rules, my wife and I went into a local antiques store just this weekend and found a K&E 4101 20-inch-long Stadia slide rule with leather case. (Full disclosure, she saw it first.) And that’s why collectors still visit the stores. More about this latest find next time…