Chronology of Time Measurement Technology

-270 Ctesibius builds a popular water clock.
-46 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.
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.