Yesterday, at the Harvest Festival at Ardenwood Historic Farm, I saw an exhibit of antique surveying instruments. Among those was a Curta mechanical calculator. Fascinating little thing. I subsequently found out that there's a Curta simulator in Flash; that these things go for about a kilobuck on eBay; and that someone out there had the chutzpah to disassemble theirs.
Back in the early 1960s, my dad was studying at the École Nationale Supérieure de l'Aéronautique in Paris. My mother told me stories about him doing his homework late into the night, while she listened to the clicking of one of these things.