First sundials appear Sundials are the oldest known timekeeping instruments in history. They first appeared in Egypt around 3500 BC and were relied upon as the primary source for accurate timekeeping throughout the world until the Middle Ages. When turret clocks began to appear in the medieval period, cathedrals and town halls continued to use sundials when correcting the time on these clocks to mean time. Later, people in the countryside set their own clocks by reference to a sundial in their gardens. Even after the invention of the domestic pendulum clock by Christiaan Huygens in 1656, all clocks still had to be set locally according to the time indicated by a sundial. Read more about sundials in the Clocktime article The first timekeepers: Telling time before the pendulum clock. Image Credit A 19th Dynasty, 13th-century BC limestone sundial inscribed with black ink. Discovered in the Valley of the Kings, Egypt. 7 in wide, 6 in tall, 1.3 in thick. Courtesy University of Basel, Egyptology Stone sundial with Liubo markings. BabelStone, CC BY-SA 3.0, via Wikimedia Commons, https://commons.wikimedia.org/wiki/File:Stone_sundial_with_Liubo_markings.jpg
