What is a Slide Rule?

Once considered one of the most valuable tools in learning the basics of advanced mathematics, the slide rule was part of the standard school equipment for junior and senior high school youth up until the 1970’s. With a history that goes back to the 17th century, the slide rule utilizes two complementary logarithmic scales to perform quick division and multiplication tasks. Prior to the mass production of pocket calculators and personal computers, slide rules were considered a more reliable means of working equations than the use of paper and a pencil.

The basic concept of the slide rule was developed in the early years of the 17th century, due to the efforts of Edmund Gunter of Oxford. Earliest designs for the device included a single scale of logarithms, and was arranged to allow for simple multiplication and division. During the 1630’s, William Oughtred of Cambridge initiated the practice of utilizing two of the Gunter slide rules in a side by side approach. This led to the creation of the slide rule design that is familiar to most people.

Along with the two logarithmic scales, more advanced slide rules often included features that helped with other types of calculation. The binary slide rule was first offered in the 1930’s and made functions involving the addition and subtraction of fractions easier. Over time, more comprehensive slide rule options allowed use of the device with such tasks as working trigonometric equations, square roots, and exponentials

While the rectangular shaped linear slide rule is the most commonly recognized design, there are actually other versions, many of them allowing for a wide range of calculations. Circular slide rules were often used in industries such as construction, architecture, and other professions that required precise mathematical calculations. The cylindrical slide rule is still utilized in some parts of the world, and like the standard slipstick rule is easy to operate.

Even though the slide rule has declined in use today, there are still fans of the device. One of the main advantages of keeping a slide rule handy is that the device requires no power source and no upgrades in order to accurately process equations.