What clock feature did Leonardo da Vinci design to improve the accuracy of a mechanical clock?

Leonardo da Vinci designed a pendulum escapement to improve the regulation of a mechanical clock.

An escapement controls the release of energy from a clock’s driving mechanism. It lets the gear train advance in measured steps while sending regular impulses to the timekeeping element. In Leonardo’s drawings, a pendulum-like regulator was linked to an escapement mechanism, showing his interest in making clock motion more uniform.

Leonardo’s design predates Galileo Galilei’s famous pendulum studies and Christiaan Huygens’s first successful pendulum clock by decades. However, Leonardo’s pendulum escapement was not a completed, working pendulum clock. The drawings show an important mechanical idea, but the practical accuracy and stability of later pendulum clocks depended on further developments.

The design should not be called a quartz clock feature: quartz regulation belongs to 20th-century electronic timekeeping. Nor should Leonardo be credited with inventing the mechanical clock itself, which had already developed in medieval Europe. His contribution was a proposed improvement to regulation and escapement design.