Not only was Gottfried Wilhelm Leibniz a very significant arts scholar and mathematician, he was also really talented when it came to technics. To accelerate and simplify the tedious calculating on paper, he invented a so called four species calculating machine - an apparatus that was able to conduct the four basic arithmetic operations mechanically. Leibniz thought it was "... worthless to waste the time of outstanding people with menial calculating tasks, because with the usage of a machine, even the most simple person would be able to write down the results correctly."
For his decimal calculating machine, Leibniz conveyed the single steps of solution from calculating in writing systematically into the mechanical process of counting which is conducted by cylindrical rollers with ten different sprockets of different sizes in combination with cogs. The so called "stepped drums", invented by Leibniz, can be twisted with a crank and cogs of different sizes around 0 to 9 sprockets further. Depending on the direction of movement, these can be either added or subtracted. The multiplication is conducted as a reocurring addition, the division as an ongoing subtraction. The result of the respective arithmetic operation can be read off little round discs.
On 1 February 1673, Leibniz introduced the Royal Society in London to a functioning model of his revolutionary calculating machine (looking rather like a wooden box with a crank and several cogs) - and noted thereto: "This in a crude model tested machine will now be perfected in brass."
Leibniz advanced his prototype and built three more models, there is no record about the whereabouts of these machines though. He developed his fourth machine, the so called "machina arithmetica", in 1690. After his death on 14 November 1716, this one fell into oblivion and was only rediscovered 1894 in the attic of the University Church of Göttingen and nowadays ranks among the most valuable cultural treasures of the 17th century. The 14 kilogramme heavy original is preserved at the Gottfried Wilhelm Leibniz Library - National Library of Lower Saxony (GWLB) in Hannover and can be seen on the first floor alongside the private working library of Leibniz in a glassy gallery.