Timeline of time measurement technology

270 BC - Ctesibius builds a popular water clock
46 BC - Julius Caesar and Sosigenes develop a solar calendar with leap years
1502 - Peter Henlein builds the first pocketwatch
1582 - Pope Gregory XIII, Aloysius Lilius, and Christopher Clavius introduce a Gregorian calendar with an improved leap year system
1656 - Christian Huygens builds the first accurate pendulum clock
1676 - Motion works and minute hand introduced by Daniel Quare
1680 - Second hand introduced
1737 - John Harrison presents the first stable nautical chronometer, thereby allowing for precise longitude determination while at sea
1928 - Joseph Horton and Warren Morrison build the first quartz crystal oscillator clock
1946 - Felix Bloch and Edward Purcell develop nuclear magnetic resonance
1949 - Harold Lyons develops an atomic clock based on the quantum mechanical vibrations of the ammonia molecule
2008 - Launch date for the Primary Atomic Reference Clock in Space.

See also: clock