https://en.wikipedia.org/wiki/Stepped_reckoner

The stepped reckoner was based on a gear mechanism that Leibniz invented and that is now called a Leibniz wheel. It is unclear how many different variants of the calculator were made. Some sources, such as the drawing to the right, show a 12 digit version.[4] This section describes the surviving 16 digit prototype in Hanover.

The machine is about 67 cm (26 inches) long, made of polished brass and steel, mounted in an oak case.[1] It consists of two attached parallel parts; an accumulator section to the rear, which can hold 16 decimal digits, and an 8 digit input section to the front. The input section has 8 dials with knobs to set the operand number, a telephone-like dial to the right to set the multiplier digit, and a crank on the front to perform the calculation. The result appears in the 16 windows on the rear accumulator section. The input section is mounted on rails and can be moved along the accumulator section with a crank on the left end that turns a worm gear, to change the alignment of operand digits with accumulator digits. There is also a tens-carry indicator and a control to set the machine to zero. The machine can:

add or subtract an 8-digit number to / from a 16-digit number

multiply two 8-digit numbers to get a 16-digit result

divide a 16-digit number by an 8-digit divisor

https://en.wikipedia.org/wiki/Curta

The Curta is a small mechanical calculator developed by Curt Herzstark. The Curta's design is a descendant of Gottfried Leibniz's Stepped Reckoner and Charles Thomas's Arithmometer, accumulating values on cogs, which are added or complemented by a stepped drum mechanism. It has an extremely compact design: a small cylinder that fits in the palm of the hand.

Curtas were considered the best portable calculators available until they were displaced by electronic calculators in the 1970s.[1] .....The Curta was conceived by Curt Herzstark in the 1930s in Vienna, Austria. By 1938, he had filed a key patent, covering his complemented stepped drum, Deutsches Reichspatent (German National Patent) No. 747073. This single drum replaced the multiple drums, typically around 10 or so, of contemporary calculators, and it enabled not only addition, but subtraction through nines complement math, essentially subtracting by adding. The nines' complement math breakthrough eliminated the significant mechanical complexity created when "borrowing" during subtraction. This drum would prove to be the key to the small, hand-held mechanical calculator the Curta would become.

His work on the pocket calculator stopped in 1938 when the Nazis forced him and his company to concentrate on manufacturing precision instruments for the German army.[2

http://www.vcalc.net/cu.htm

https://newatlas.com/curta-death-camp-calculator/45506/