My father recently gifted me a prize posession, his Keuffel & Essen Duplex Log Log Decitrig Slide Rule.

Dad bought the slide rule in 1944 when he started studying engineering at Cornell. He still has the case and instructions to care for it.

Slide rules had been around a long time. The first was invented in the 1620s by William Oughtred. It leveraged the discovery of logrithmic scales to multiply and divide.

It was enhanced in 1859 by a French artillery officer and took on its modern form. It became standard kit for engineering students like my father until the 1970s.

The company most associated with the slide rule, Keuffel & Essen (K&E), was founded in 1867 by two German immigrants to manufacture scientific measuring equipment. K&E started making their own slide rules in 1891.

Today, it’s hard to understand the passion this tool once engendered. I asked some of dad’s friends (all retired engineers in their 80s) if they remembered slide rules. Two literally reached into their desks and took them out. Another had kept the manual.

No one taught you how to use a slide rule. You figured it out or you failed. One man said he dropped his slide rule onto the subway tracks. He considered it so valuable that he leapt down to retrieve it. “Someone told me I was crazy,” he said.

Slide rules were used for some of the biggest scientific developments in history. The Manhattan Project used a circular slide rule to calculate the fallout from the atomic bomb. German scientist Wernher von Braun bought two Nestler slide rules in the 1930s and was still using them in 1969 when he worked on NASA’s effort to land on the moon.

People talk about “disruption” in business these days, but it’s hard to imagine anything more disruptive than the disappearance within a decade of a technology used for three-and-a-half centuries.

Hewlett-Packard unveiled its first desktop calculator in 1968. By 1974 the HP-35 handheld was available for $395. By 1976 the price for the pocket calculator had plummeted to $25.

That doomed the slide rule and K&E shut down its manufacturing operations the same year. Sensing perhaps its importance to history, the company donated its equipment to the Smithsonian museum.

A decade earlier, K&E had commissioned an analysis of what the future held. It predicted that within 100 years Americans would live in cities inside domes and watch 3D television.

What the report didn’t anticipate was the invention of the calculator a year later.

The story is a great reminder of how long things can remain the same and then how suddenly and dramatically everything can change.