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He noticed that each swing took about the same time whether the arc was wide or narrow. This regularity became the basis of the pendulum clock, which made clocks far more accurate than earlier weight-driven mechanisms.
Every timekeeper pairs something that moves or flows at a steady rate with a way of counting or marking it. The steady thing can be a shadow, dripping water, falling sand, a burning candle, or a swinging weight. A clock is only as accurate as its underlying process is regular, so each improvement in timekeeping came from finding a steadier process to count.
Timekeeping devices developed as a chain in which each new device fixed the conditions under which the previous one broke down. Sundials were useless at night and under clouds, so people turned to water clocks. Water clocks froze or needed refilling, which led to sand glasses and fire clocks, and all of these needed constant tending, which drove the move to self-running mechanical clocks.
In antiquity, daylight was divided into twelve hours whatever the season, so a summer hour was longer than a winter hour and night hours shrank to match. The measuring tools were built around this convention, and water clocks had to be adjusted as the seasons changed. Only mechanical clocks, which tick at one constant rate, established the equal hour, which shows that the unit itself was shaped by the technology.