In **1622**, four hundred years ago, English clergyman and amateur mathematician **William Oughtred** invented the **Slide Rule**. It was one of most important inventions in the Age of Enlightenment and the Industrial Revolution, used in mathematics, engineering, physics, and many other sciences.

Like the **navigation compass** *(11th century)*, the **printing press** (1440), the **microscope** (1590), the **telescope** (1608), the **manual typewriter** (1867), and other technological leaps, the slide rule remained in constant use from its invention until the age of transistors (1947) and microchips (1958). It was digital computing that made these devices expendable, not because they stopped working. For almost three hundred and fifty years until the first portable calculators in 1970, the slide rule was **THE** mathematical computer.

The slide rule was used in the construction of buildings, bridges, ships, trains, cars, airplanes, and other constructions. **Isaac Newton used them to solve cubic equations**. **Albert Einstein used them to do his groundbreaking work**. It was used by NASA, both by **Katherine Johnson to compute flight trajectories** and by **the crew of the Apollo 13 to do the calculations** that brought them home safely.

As with other inventors and inventions *(e.g. Johan Gutenberg and the printing press)*, Oughtred didn’t create every part of the slide rule. He took the works of others before him and put them together in a way that made the invention useful and indespensible. The slide rule provided the ability to do fast and accurate calculations which previously were prone to error when done by hand. The slide rule he invented was a simple design, refined over the next 300 years with additions like Newton’s cursor.

Slide rules aren’t limited to logarithms and trigonometry. There are slide rules for engineering, airplane pilots, music, chemistry, astronomy, welding, metallurgy, and many other uses. They’re portable and accurate quick references. The slide rule and the other inventions mentioned above still work *(the microscope, the typewriter, et al)*. They only fell out of use because newer inventions do the work faster. *(Do a least squares regression with a slide rule? Only if there’s no other way!)*

Over the coming months, the plan is to write multiple posts on Slide Rules: the mathematics that made them possible, the invention, how to do math on a slide rule, the different types, how to make your own slide rules, where you can still buy them, and possibly others.

For now, a little fun: below the fold, slide rules in popular culture.

In a Slide Rule discussion group, someone recently asked if there were any songs that mentioned them. I knew about Sam Cooke’s song, but not any of the others offhand. There aren’t enough to create a *“Slide Rule’s Greatest Hits”* album, but maybe enough for an EP. If anyone knows any more, let me know. *(Sorry, there’s no better version of the CSNY song on youtube.)*

**Tom Lehrer, “The Slide Rule Song” (1951)**

**Sam Cooke, “What A Wonderful World (1960)**

**Connie Francis, “He’s Just a Scientist” (1967)
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**Gordon Lightfood, “In My Fashion” (1982)**

**Crosby Stills Nash & Young, “Driving Thunder” (1988)**

**Headstones, “Done The Math” (2017)
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There’s obviously this one. Again, I can’t find a better version:

**MIT Engineers’ “Beaver Call” fight song (unknown origin date)
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The **slide rule also appeared in Marvel’s Iron Man comics**, circa 1964.

An odd sidenote:

For all the computerization that schools, colleges, businesses and governments have gone, and manual tools gone by the wayside, you will have absolutely no problem finding or purchasing **computer flow chart templates** for designing systems on paper. And despite computer aided design (CAD) being easy enough now for anyone to use, and around since the 1980s, **T-squares and Set Squares** for draughting are still for sale. What I learnt in my high school draughting classes were among the most useful skills I was ever taught.

Some Old Programmer says

The conversion to calculators was very fast. My first year in High School (1975-76) included use of a slide rule in advanced chemistry. And by the time I graduated, I had a TI-58, which was a big deal for a poor kid.

Rob Grigjanis says

I remember slide rules from high school, and maybe the first couple years undergrad. Still have my last one lying around somewhere. While appreciating their value from a historical perspective, I have zero nostalgia for them. Calculators were a blessing.

jrkrideau says

I got my first slide-rule in Grade 9 and may have been still using one in grade school. Calculators were expensive !

anat says

Until 1981 calculators were forbidden in my school (on grounds of equity). So I used my mother’s slide rule. (She also taught me an efficient paper and pencil algorithm for calculating square roots ). The following year I got my first scientific calculator.

jrkrideau says

International Slide Rule Museum

Also Thoney’s discussion is interesting

Sliding to Mathematical Fame