A taxonomy of timekeeping


5,000-4,000BC? supposed Sumerian timekeeping

3,500BC? obelisks

1,500BC sun dial

shadow clock

sun dial

600BC? Egyptian merkhet star clock


1,500BS Amenhotep I water clock buried 325BC Greek clepsydra (water thief) water drippting into tank with float hourglass


strings with pebbles on gong candle oil lamp


1310? verge and foliot (15 minutes per day) 1500-1510 Peter Heinlen spring drive 1582 Galileo observes pendulum isochronism 1583 Galileo's pin wheel escapement 1656 Huygens first pendulum clock (< 1 minuter per day) 1671 Clement's anchor or recoil escapement 1675 Huygens balance wheel and spring (portable clock 10 minutes per day) 1721 George Graham's compensating pendulum (1 second per day) 1761 John Harrison (0.3 seconds per day on a rolling ship) 1889 Siegund Riefler (0.001 second per day) 1898 Rudd's free pendulum principle


1921 W. H Shortt master-slave clock


1920 onwards quartz crystals


1955 NPL cesium atomic frequency standard
Pages written by Adrian Johnstone, last updated 1 July 2009.