The Greeks used a sundial called “pelekinon”. These sundials are marked to predict time accurately throughout the year. They built a more accurate sundial based on their knowledge of geometry. An ancient Egyptian sundial from the 8th century and a Greek sundial are still in existence today. Water clocks along with sundials are known to be the oldest time-measurements devices. The bowl-shaped outflow is the simplest form of a water clock and is known to have existed in Babylon and in Egypt around the 16th century BC. Other regions of the world, including India and China, also have early evidence of water clocks, but the earliest dates are less certain. Some authors, however, claim that water clocks appeared in China as early as 4000 BC. (Cowan, 1958)
Ctesibius or Ktesibios or Tesibius (Greek: Κτησίβιος) (fl. 285–222 BC) was a Greek inventor and mathematician in Alexandria, Ptolemaic Egypt. (As of 2008, 1768–2010) He improved the