Brunsviga model 13Z lever set mechanical calculator, made by Brunsviga Maschinenwerke AG in Germany, 1945-1955.

The Brunsviga model 13Z mechanical calculator could perform the four basic arithmetic calculations: addition, subtraction, multiplication and division. They are heavy machines and would be kept on a desktop.

The model 13Z was a pinwheel calculator. Numbers would be inputted using the pin wheels (gears that are covered by the curved middle section of casing). In this photograph, the number 4 has been inputted.

The large crank handle on the right of the machine performed addition and multiplication, subtraction and division, depending on whether it was turned backwards or forwards. The three smaller cranks were used to reset the displays to 0. The middle row of digits is the input register, where numbers up to 1x10^9 magnitude (billion) could be inputted. The bottom row of digits is the output register and could display numerical answers up to an order of 1x10^12 (trillion) magnitude.