What calculating machine did Leonardo da Vinci sketch with numbered wheels and gears?

Leonardo da Vinci sketched a mechanical calculator with numbered wheels and gears.

The design appears in Leonardo’s Codex Madrid I, a manuscript compiled around 1490–1500. Its geared wheels were intended to represent decimal values and perform arithmetic through controlled rotation. The device is usually described as a design rather than a proven working calculator built by Leonardo.

This concept is often connected with later calculating machines, but Leonardo did not invent the electronic calculator or the first commercially successful mechanical calculator. Blaise Pascal’s Pascaline, developed in the 1640s, is a later calculating device with clearer evidence of construction and use.

Leonardo’s calculator is significant because it shows how Renaissance engineers applied gear trains to abstract numerical operations. The surviving drawings provide evidence for the idea, while details of its exact operation remain subject to reconstruction.