What calculating device did Leonardo da Vinci design with numbered wheels for arithmetic?

Leonardo da Vinci designed a mechanical calculator using numbered wheels to represent arithmetic values.

His drawing, made in 1502, shows a system of geared wheels arranged to support calculations. Turning one wheel could advance another by a controlled amount, reflecting the carrying process used in addition. The mechanism is often described as an early calculator design, although historians debate how completely the drawing specifies a practical working machine.

Leonardo’s device should not be confused with an abacus, which represents numbers with movable beads, or with later electronic calculators. It was a proposed geared mechanism, and no surviving original machine proves that Leonardo built a finished calculator.

The design is important because it shows Leonardo applying mechanical engineering to abstract numerical operations. It belongs to the same intellectual world as his studies of gears, motion, accounting, and automated machinery.