Telling time By tkonarska 3000 BCE People start using the obelisk to tell time 1500 BCE Water clock is invented 300 BCE People start using the sundial Jan 1, 1000 The hour glass is used Jan 1, 1300 Mechanical clocks invented. Jan 1, 1400 watches invented Jan 1, 1884 Greenwich Mean Time Jan 1, 1972 Universal Time Coordinate used