In The Time Keeper, Dor is credited with discovering every form of timekeeping that later civilizations will develop, beginning with the charting of shadows and leading to the construction of calendars and clocks. According to The National Institute of Standards and Technology, “in every culture, some people were preoccupied with measuring and recording the passage of time” (Higgins, K., et al. A Walk Through Time. National Institute of Standards and Technology, 2004).

Early civilizations used the charting of the celestial bodies—sun, moon, planets, and stars—to determine seasons, months, and years, creating the first calendar systems. The development of clocks, the charting of the hours of each day, is a more recent development. The first recorded clocks were constructed 5,000 to 6,000 years ago in civilizations in the Middle East and Northern Africa, particularly among the Sumerians and Egyptians. These early clocks charted the passage of the sun throughout the day by charting shadows. Among the earliest clocks that were not dependent on celestial bodies were water clocks, called clepsydras or “water stealers” by the Greeks. These clocks were containers that allowed water to drip at a near constant rate, marking minutes and hours. Weight-driven mechanical clocks began to appear in Europe during the 14th century, and the first pendulum clock was constructed in the 17th century.