Mechanical Calculator

Before the digital calculator we all know today was created, people used other devices to add, subtract, divide and multiply. These tools varied from the basic abacus to complex machines like the Curta calculator. Since they do not use electricity, and instead the movement of gears and other mechanisms, we call them mechanical calculators.

In 1623, Wilhelm Schickard created the first blueprints for the Mechanical calculator. His unsuccessful attempts to construct a calculator caused him to completely abandon the project and not mention it again until he was on his deathbed eleven years later in 1635. His idea was picked up by Blaise Pascal who managed to solve all the problems that Schickard ran into, such as carrying.

Curt Herzstark thought of this variation of the mechanical calculator in the 1930’s. This calculator had the ability to do addition and subtraction. Herzstarks work on the calculator stopped in 1938 when his company was forced to manufacture measuring instruments and distance gauges for the Nazis. When it was discovered that he was the son of a Catholic woman and a Jewish man, he was taken to the Buchenwald concentration camp. There, he continued to work on the calculator by drawing the design because the warden of the camp wanted to give the calculator to Hitler after the Nazis won WWII.

Our Mechanical calculator consists of two major parts: the input, and the display.

The input relies on a leibniz wheel: a special gear that allows a gear to be turned a different number of teeth depending on its position. By positioning a gear and turning the leibniz wheel in one way, the user can add a number, and by turning it the other way, subtract it.

The display consists of several drums with numbers marked on them. The rotation of the leibniz wheels connect directly to the drums representing the 1s and 10s place, and the 100s place is connected exclusively through the carry mechanism. The carry mechanisms are gears with only 2 teeth, but the same diameter as the gears attached to the drums. This enables them to turn the gear for the next place only when a number needs to be carried over.