What Leonardo da Vinci device used water to measure the passage of time?

Leonardo da Vinci designed a water clock to measure the passage of time.

Water clocks, also called clepsydrae, measure time through the controlled flow of water into or out of a container. Leonardo studied and drew water-driven timing mechanisms, including designs that used changing water levels and mechanical indicators.

The principle was already ancient before Leonardo. Egyptian and Greek civilizations used water clocks, and later Islamic engineers created highly elaborate versions. Leonardo's contribution was his detailed mechanical investigation and adaptation of the idea for Renaissance engineering.

A water clock does not measure time through gears alone, so it differs from a mechanical clock. It also works without sunlight, unlike a sundial. Its accuracy depends on maintaining a regular flow and controlling changes caused by water pressure.