What machine did Leonardo da Vinci design to produce arithmetic calculations mechanically?

Leonardo da Vinci designed a mechanical calculator to produce arithmetic calculations through geared motion. The proposed machine used a series of wheels and gears so that turning one part could carry values into the next place.

The calculator appears in Leonardo's Codex Madrid I, a manuscript rediscovered in the twentieth century. Its mechanism is often associated with a design dated to 1493, making it an early example of a geared calculating machine. The exact purpose and operating procedure remain subjects of historical interpretation because Leonardo did not leave a complete modern-style manual.

Leonardo's calculator was not an electronic computer and is not known to have been built in his lifetime. It is also separate from his better-known self-propelled cart, which was designed for movement rather than arithmetic. Reconstructions have shown that the gear concept can be made to operate, but reconstruction does not prove that Leonardo completed a working original.