Slide Rule
I was telling a friend about Scilab, the free numerical analysis tool, and came across a university page describing other numerical tools, such as the slide rule. There is even a society that is dedicated to the preservation and history of slide rules and other calculating instruments – Oughtred Society. I think I may have used a slide rule once. I came across some Slide Rule Operating Instructions in a box of papers that my dad had, and scanned them for posterity.