I really love this kind of thing, but I can't quite explain why. This mechanical calculator was invented by Curt Herzstark — an Austrian Jew — while he was being held in Buchenwald concentration camp during the Second World War. I played with the simulator for ages, but I still can't quite figure out how you would actually use it to calculate things. It's like a slide rule; my Dad used one for years before the advent of affordable electronic calculators, but to me, it's tantamount to magic.
I'd love to have a go on a real Curta calculator though — it looks as if it has just the right amount of clicking, rattling, twirling things to play with.