Analog Computers [Basic Metrology]

In the December 2016 issue of I&M Magazine, there is a fine bit of history about the rise and fall of the slide rule [1]. The slide rule as used for multiplication and division qualifies as an analog computer, and analog computing will be the topic of this column. The best way to understand how a slide rule works is to make one. I started with a piece of semilog graph paper. Interestingly, some companies-Keuffel and Esser is an example-manufactured both slide rules and many styles of graph paper. I began with an image of semilog graph paper. The vertical axis of this paper is a logarithmic scale, while the horizontal axis is linear. I rotated the image clockwise by 90° and snipped it to produce Fig. 1. The logarithmic scale is now horizontal. I also reproduced the original labels on the top and bottom of the snippet.