Image: Kerry Redshaw
Neatorama has a fun overview of the early history of computing, discussing famous computing devices like the Antikythera Mechanism and Babbage's Difference Engine, as well as ones I'd heard of but never actually seen, like Leibniz' Stepped Reckoner.
Leibniz’s design used a special type of gear called the Stepped Drum or Leibniz wheel, a cylinder with nine bar-shaped teeth along its length. He named his machine the Staffelwalze or the Stepped Reckoner.
The machine was a marked improvement from Pascal’s design and could add, subtract, multiply, divide, and even evaluate square roots by a series of additions.
The Wonderful World of Early Computing [Neatorama]