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This timeline of time measurement inventions is a chronological list of particularly important or significant technological inventions relating to timekeeping devices and their inventors, where known.

Note: Dates for inventions are often controversial. Sometimes inventions are invented by several inventors around the same time, or may be invented in an impractical form many years before another inventor improves the invention into a more practical form. Where there is ambiguity, the date of the first known working version of the invention is used here.

Classical antiquity

c. 3500 BC - Egyptian obelisks are among the earliest shadow clocks.^[1]
c. 1500 BC - The oldest of all known sundials, dating back to the 19th Dynasty.^[2]
c. 500 BC - A shadow clock is developed similar in shape to a bent T-square.^[3]
3rd century BC - Berossos invents the hemispherical sundial.^[4]
270 BCE - Ctesibius builds a water clock.

Medieval era

11th century - Sets of hourglasses were maintained by ship's pages to mark the progress of a ship during its voyage
11th century - Large town clocks were used in Europe to display local time, maintained by hand
1335 - First known mechanical clock, in Milan
1502 - Peter Henlein builds the first pocketwatch
1522 - The Portuguese navigator Ferdinand Magellan used 18 hourglasses on each ship during his circumnavigation of the globe.^[5]

Modern era

1656 - Christiaan Huygens builds the first accurate pendulum clock.^[6]
1676 - Daniel Quare, a London clock-maker, invents the repeating clock, that chimes the number of hours (or even minutes).^[7]
1680 - Second hand introduced
1737 - John Harrison presents the first stable marine chronometer, thereby allowing for precise longitude determination while at sea
1850 - Aaron Lufkin Dennison starts in Roxbury, Mass.U.S.A. the Waltham Watch Company and develops the American System of Watch Manufacturing.
1884 - International Meridian Conference adopts Greenwich Mean Time for consistency with Nevil Maskelyne's 18th century observations for the Method of Lunar Distances
1893 - Introduction by Webb C. Ball of the General Railroad Timepiece Standards in North America: Railroad chronometers
1921 - The Shortt-Synchronome free pendulum clock becomes the first clock more accurate than the rotation of the Earth
1927 - Joseph Horton and Warren Marrison describe the first quartz clock at Bell Telephone Laboratories.^[8]
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
1983 - Radio-controlled clocks become common place in Europe
1994 - Radio-controlled clocks become common place in USA