[masraum]

Originally posted by Don Plumley
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There was an article I read in Scientific American last month that talked about slide rules -- how airplanes and spacecraft were designed with them. The biggest issue (I've never used one) was order of magnitude. You didn't know if the answer was 250.0 25.00 2.500 .2500 etc. So users had to be good at rough approximation to validate their work. This meant they had to have an intuitive understanding of the underlying math, something which is masked by calculators and computers.

Yep, math is cool. I've got a Pickett slide rule (very basic) and 6 or 7 Japanese abacii.

Weirdly enough the earliest known abacus is actually Roman, and the Chinese, Japanese, Russians, and Roman versions are all a little different.