History of Computers - Slide Rule

This page was created by Geoff Dunn.

The slide rule is an analog mechanical computer invented in 1622. It was used widely for calculations up until the 1970s when the scientific calculator was invented, creating a much easier and more convenient way to calculate.

Overview

The logarithm, invented by John Napier and later published in 1614, was originally for the purpose of quick calculations of multiplication and division problems using addition and subtraction. In 1620, Edmund Gunter, an English mathematician and astronomer, had the idea that it would be helpful to have a rough scale of these logarithms, and so he put the logarithms proportionately on a line and called this collection the logarithm scale. Later, Reverend William Oughtred put two of these lines side by side and used the two scales together by sliding each one for multiplication and division. Because he was the first to do so, he is considered the inventor of the slide rule. Oughtred first invented the circular slide rule and then later the straight slide rule; he also introduced the use of "x" as a sign of multiplication and the abbreviations "sin" and "cos" for sine and cosine. In the course of history, the slide rule was changed from Oughtred's original design to a more modern one made of two bars holding a sliding bar in between them. The slide rule was used for the next 300 years as a reliable and choice instrument for calculation.

Significance

The significance of the slide rule lies in many areas of history. Initially, it was used for scientific and mathematical calculations. Years later, however, it was used in many areas of science, such as for the calculation of artillery trajectories and as a simple measuring tool for engineers. In WWII, aviators used the slide rule to calculate the range, fuel use, and altitude of aircrafts. In fact, in the 20th century, it has been the symbol of engineers. Wernher Von Braun, a German scientist working for the United States during the Space Race, did not use any other calculation device aside from the slide rule; many other scientists during the time also relied on the slide rule. Man was able to fly into space and reach the moon with calculations done with the slide rule. It also led to many other inventions, such as Global Positioning Satellites (GPS), cordless power tools, freeze-dried food, fiber optics, satellite dish technology, ear thermometers, fire-resistant fabrics, smoke detectors, and many more. The Space Race, arguably driven by the slide rule because of its important role, furthered the development of computers. The slide rule's role is great and, without it, the world would be much less developed and many of our technologies would not yet exist, because people would not have been able to make such large calculations so quickly without the slide rule.