What calculating machine did Leonardo da Vinci sketch with a series of geared wheels?

Leonardo da Vinci sketched a mechanical calculator using geared wheels to represent and perform numerical operations.

The device is commonly described as an adding machine. Its gears were arranged so that movement in one place could carry into the next place, much like carrying in written arithmetic. The concept shows Leonardo applying mechanical transmission to calculation rather than relying only on written numerals or counting boards.

Leonardo’s original notes do not provide a complete operating manual, and historians debate how fully the device could have worked. A modern reconstruction demonstrated that the gear arrangement could perform addition, but reconstruction is not evidence that Leonardo built a finished calculator.

The design is therefore best understood as an early mechanical-calculation concept. It should not be confused with electronic calculators or with the abacus, which performs calculation through manually moved beads.