What mechanical calculator did Leonardo da Vinci sketch with geared wheels for arithmetic?

Leonardo da Vinci sketched a mechanical calculator with geared wheels intended to support arithmetic operations.

His notebooks contain a design using interlocking gears that could represent numerical quantities and transmit rotational movement from one wheel to another. The machine is often described as an early calculator concept because its mechanism resembles the place-value action required for carrying between digits.

The drawing was discovered and interpreted centuries after Leonardo’s death. It is not certain that he built a complete working calculator, and historians debate the exact operation intended by the sketch. Those limits matter: the design is evidence of mechanical calculation as an idea, not proof of a commercially usable Renaissance calculator.

The concept predates later calculating machines such as Blaise Pascal’s Pascaline, introduced in the 17th century. Leonardo’s contribution was to apply precision gear trains to numerical representation, linking his interests in clocks, motion, engineering, and mathematical instruments.