Two scales are calibrated identically so that, on each, the distance from the "1" point to any point on the scale is proportional to the logarithm of the number represented by that point. Since log (a.b) = log a + log b, the multiplication a.b can be performed by setting the "1" point of the scale (1) against a on scale (2), then reading off the number of scale (2) opposite b on scale (1). Division is performed by revering the procedure.
In practice, slide rules have several different scales for different kinds of calculation, and a runner (cursor) to permit more accurate readings. scales.
Related category COMPUTERS, ARTIFICIAL INTELLIGENCE, AND CYBERNETICS
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