The object for October is the slide rule. Mathematicians, scientists, engineers, and many others used this mechanical device to solve math problems before the invention of the electronic calculator. The engineers who built Ohio's canal, railway, and highway system used slide rules; so did the scientists and engineers who sent Neil Armstrong to the moon.

Slide rules commonly are made of veneered wood or bamboo, plastic, or metal. The shape and length of the ten-inch-long rule shown here is more common, but circular and round rules and a variety of sizes have been used.

The inventor of the slide rule is a subject of debate, but the Reverend William Oughtred, an English clergyman, frequently is credited, in part based on his book, Circles of Proportion and the Horizontal Instrument, which was published in 1632.

After nearly 350 years of use, the slide rule met its demise in 1972. It was replaced by the Hewlett-Packard HP-35 electronic pocket calculator. This portable, lightweight device could do more calculations more quickly and with more accuracy and precision than the slide rule. Almost overnight, slide rules passed into disuse and became collectors' items.

For more information on logarithms and using slide rules, see:
http://www.sliderule.ca/intro.htm

Form more information on slide rules and slide rule collecting, see:
http://www.oughtred.org

For more information on the HP-35 calculator, see:
http://www.hpmuseum.org