What calculating device did Leonardo da Vinci design using linked rods and numbered wheels?

Leonardo da Vinci designed a mechanical calculator using linked rods and numbered wheels.

A drawing in the Codex Madrid I, rediscovered in the 1960s, shows a calculating machine with a series of geared wheels. The mechanism appears intended to perform addition through carrying from one decimal place to the next. It is often described as an early mechanical calculator concept.

Leonardo’s notes do not provide enough information to prove that he completed or operated a full working calculator. Reconstructions have been made from the drawing, but historians distinguish between a surviving design and a documented working machine.

The concept belongs to a wider history of mechanical calculation. Blaise Pascal’s Pascaline, built in the 1640s, is generally credited as the first known mechanical calculator produced in quantity or demonstrated as a practical calculating instrument. Leonardo’s design therefore represents an earlier idea, not a modern electronic calculator.