Beredsamkeit ist die Kunst, so von den Dingen zu sprechen, daß jedermann gern zuhört.

marc kjerland posted a photo:

One of the first mechanical calculators, made in 1645 by 19-year-old Blaise Pascal. Lets you add and subtract with minimal physical effort! The gears only turn in one direction, so you had to use the method of nines' complement. They were better at arithmetic in those days.