Circular Slide Rule

To multiply two numbers and , slide the inside scale so that the 1 on it is over on the outside scale. Find on the inside scale; then is across from on the outside scale.


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This slide rule uses the identity .
[1] J. Bryant and C. Sangwin: How Round Is Your Circle?: Where Engineering and Mathematics Meet, Princeton, NJ: Princeton University Press, 2008, pp. 240–241.
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