Recently I got interested in mechanical devices, especially mechanical calculators, also known as arithmometers.
They represent the first devices which were reliable enough to be used in offices. Although the name “arithmometer” was given later on to a specific device built by Louis Payen somewhere around the year 1887, their ancestor device, the Pascaline, invented in 1645, and also successor devices bare the same name.
Before the invention of the arithmometer, mathematical calculations were performed by paid human “computers.” About twenty companies produced the original arithmometer design, among which there were the Bollée, and its successor, the Millionaire Machine. These were the only devices that could perform automatic calculations of all four basic mathematical operations, most of them by means of a single turn of the crank per number (except for division, which requires turning the crank until the machine stops on its own). Unfortunately, very few models survived pass World War II. In the scientific area, we have the famous Difference Engine.
Regarding mechanical calculators you might be familiar with (see the video below of a mechanical calculator in action), in 1873 a swedish man named Willgodt Theophil Odhner, who moved to Russia, came up with a new design for an arithmometer for the masses. It was named simply The Odhner, and its production started in 1890. The design was so successful that it was cloned by manufacturers all over the world, with familiar names like Brunsviga, Facit, Walter, Triumphator, and so on.
P.S. The video does not belong to me, I am only showcasing it as a prime example for the functionality of a typical mechanical calculator.