When Slide Rules Ruled

By Paul Gipe

I don’t remember how slide rules came up in a conversation recently. It may have been when Nancy recalled her dreaded chemistry classes in college and noted that she never learned how to use the complimentary slide rules they were given in the class.

What? I fumed. How could she get through university without a slide rule? Turned out no one else on the Zoom call—all college graduates–knew how to use them either.

Since it was Zoom, I reached under my desk for my very dusty slide rule and pulled it out of the case and proudly displayed it.

Ok, I am a nerd. I’ve noted it before.

While I don’t use a slide rule—and haven’t for going on five decades–I do remember how to multiply and divide on it.

At one time it was my constant companion.

I bought a Post Versalog 1460 made by Hemmi of Japan in the fall of 1968 when I started at General Motors Institute of Technology. It was expensive for a poor kid from a blue collar family, but it had then and still does have a feel of quality craftsmanship. With its celluloid over bamboo construction it was a marked contrast to the much cheaper Picket slide rule made out of aluminum that was also then on offer. My slide rule came with a handsome leather carrying case with a belt loop, though we were under strict orders to never be caught wearing one our belt—a sure sign of a neophyte.

That Post Versalog kept me company for the two years I stuck it out at GMI. I still keep it within reach at my desk, though it’s now relegated to a hidden shelf where it gathers dust.

Nancy’s father got a PhD in chemistry from Caltech. He had a good slide rule too. We still have it as a memento. It’s tucked away in a filing cabinet. He used his Keuffel & Esser (made in the USA back when we made stuff here) professionally and it shows signs of heavy wear. It too is celluloid over bamboo. K&E began manufacturing his slide rule in the late 1930s or about the time he was at university. His leather case is much more elegant than the case for my Post Versalog and it doesn’t have a belt loop. Engineers in his day didn’t wear their slide rule, they carried it and his well-worn case shows signs of regular use.

I am proud to say that after examining my slide rule the “Post” and “Hemmi Japan” markings on the cursor (runner) are nearly rubbed off. I used it daily for those two years. I used it infrequently after that and by the time I wrote my first wind book in the early 1980s I had migrated to a simple Texas Instrument’s calculator where I could do regression analysis.

Though no one uses them today, they were the principle tool of engineers and scientists until the advent of electronic calculators. As many as 40 million slide rules may have been manufactured in the 20th century alone. Imagine that all of the world’s modern bridges and buildings more than 50 years old were built with the aid of slide rules.

I’ve mentioned slide rules and the importance of knowing how to use significant numbers in every one of my wind books, including my last in 2016. The lessons learned from the use of the slide rule are just as important today as they were when I started my career long ago, even if we don’t use the slide rule itself.

There are many web sites devoted to the slide rule, including Wikipedia’s Slide rule page. The International Slide Rule Museum (ISRM) has an extensive web site where you can find details, including user manuals, for most commercial slide rules. It’s not to be confused with the The Oughtred Society (named after the inventor of the modern slide rule in the 17th-century) or Other slide rule sites, an old-fashioned html list of web sites on slide rules.

If you’re a hard-core nerd, All about Slide Rules by the Oughtred Society is a 111-page document that takes you through the different kinds of slide rules and how and why they were developed.

The slide rule was a fine machine. It’s sad to see it go the way of the Dodo.