Arithmaurel
The Arithmaurel was a mechanical calculator that had a very intuitive user interface, especially for multiplying and dividing numbers because the result was displayed as soon as the operands were entered.
[1] It received a gold medal at the French national show in Paris in 1849.
The heart of the machine uses one Leibniz stepped cylinder driven by a set of differential gears.
[5] This is the design that won a gold medal at the Exposition nationale de Paris in 1849.
All the registers are located on the front panel, the reset mechanism is on the side.
Arithmaurel: the stems at the top are for entering the operands and the dials with their keys are for entering the operators