The history of the slide rule spans roughly 350 years from beginning to end. The earliest slide rules were simple physical rulers but marked with special scales based upon the concept of the logarithm and were used to quickly perform multiplication and division calculations with an accuracy of a few digits. Invented in the early 17th century using two sliding scales, by the start of the 19th century additional scales had been added to slide rules to provide access to squares, roots, and values of trigonometric functions. By the middle of the 20th century many slide rules were double-sided with highly-accurate scales and manufactured from a variety of materials. Models could be found that had incorporated one or two dozen different scales on a single slide rule for performing a wide variety of calculations; the slide rule had become a standard tool used by students and professionals for computations typical of mathematics, science, engineering, and many business practices. Then in the 1970s, seemingly overnight, electronic calculators became easily attainable by the general public and the production and sales of slide rules vanished.

Spiral Long Scale Manheimm Style Pocket Size Modern Slide Rule Helical Long Scale
The slide rules in the collection presented here mostly have been found in antique shops, flea markets, and through local dealers in the Midwestern United States, typically within a few hours drive from Chicago. With many early American slide rule manufacturers and retailers having been based in Chicago, the search has been a very fruitful activity for this enthusiastic hobbyist.
Other slide rules in the collection have been found during various trips around the U.S. and some have been obtained from overseas and elsewhere in the U.S. via online vendors.
The original motivation for creating this web site was to help me in keeping track of the items in the collection and to be able to share the collection with other slide rule connoisseurs. As time went on, however, it became clear that many young people are starting to collect slide rules and are interested in learning how to use them. And while I was actually trained in their use and the mathematics behind them, anyone under the age of about 65 likely never had that experience. Hence the site has evolved to include introductory material in the opening chapters in addition to a selection of special groupings and stories about various subgroups of the collection.