http://en.wikipedia.org/wiki/File:Prosthaphaeretic_Slide_Rule2.svg

although they called it a Prosthaphaeretic slide rule for some strange reason:

http://findarticles.com/p/articles/mi_qa3950/is_200401/ai_n9372466/

]]>Not entirely outdated. Occasionally I lose the remote!

Also, I’ve been looking up abacuses (abacii?) after the comment about the Roman abacus on the other thread and there are some differences in historical abacuses severe enough to qualify as different methods of multiplication. I think we could reach 35.

]]>Speed. If you’re an astronomer with no calculators, would you want to multiply piles of numbers using the standard multiplication algorithm or would you want to (1)lookup tables (2)add the logs and (3)do a reverse lookup?

Addition is less prone to errors than the multiplication and addition together.

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