Leonardo da Vinci studied a pendulum as a possible way to make timekeeping more regular.
His notebooks contain drawings and observations of pendulum motion. Leonardo was interested in the regularity of repeated swings and in how that motion might regulate a clock mechanism. These studies predated the first successful pendulum clocks by more than a century.
Leonardo did not build the first pendulum clock. Christiaan Huygens patented a practical pendulum clock in 1657, using a pendulum as the regulator of the clock’s escapement. Huygens’s work turned the principle into a highly accurate timekeeping system, whereas Leonardo’s surviving material consists mainly of investigations and proposed mechanisms.
A pendulum is not itself a complete clock. It must work with an escapement, gears and a power source. Leonardo also studied water clocks and other time-measuring mechanisms, so his pendulum drawings belong to a larger program of research into motion, oscillation and mechanical regulation.