text: History of Telling Time
  Prehistoric man, by simple
  observation of the stars, changes in the seasons, day and night
  began to come up with very primitive methods of measuring time.
  This was necessary for planning nomadic activity, farming, sacred
  The earliest time measurement
  devices before clocks and watches were the sundial, hourglass
  and water clock. Find out more about these
  types of clock here
  The forerunners to the sundial
  were poles and sticks as well as larger objects such as pyramids
  and other tall structures. Later the more formal sundial was
  invented. It is generally a round disk marked with the hours
  like a clock. It has an upright structure that casts a shadow
  on the disk - this is how time is measured with the sundial.
  The hourglass was also used
  in ancient times. It was made up of two rounded glass bulbs
  connected by a narrow neck
  of glass between them. When the hourglass is turned upside down,
  a measured amount of sand particles stream through from the
  top to bottom bulb of glass. Today's egg timers are modern versions
  of the hourglass.
  Another ancient time measurer
  was the water clock or clepsydra. It was a evenly marked container
  with a spout in which water dripped
  out. As the water dripped out of the container one could note
  by the water level against the markings what time it was.
  A huge advance occurred in
  the 1300’s when mechanical clocks, which used weights
  or springs, began to appear. At first, they had no faces, and
  no hour or minute hands; rather, they struck a bell every hour.
  Later, clocks with hour, and then minute hands began to appear.
  These early mechanical clocks worked by using an escapement,
  a lever that pivoted and meshed with a toothed wheel at certain
  intervals. This controlled the movement, or "escape"
  of either the weights or the springs that were powering the
  clock, in order to regulate the speed at which the gears and
  wheels which measured the time turned.
  In the 1400’s, another
  important discovery in timekeeping was made: it was learned
  that coiled springs, which used small coiled springs unwinding
  at a speed controlled by an escapement, were able to move the
  hands on a clock as well as weights or springs of previous,
  larger clocks. This discovery made smaller clocks, and later
  Then, in 1656, Christiaan Huygens
  invented the pendulum clock, which used weights and a swinging
  pendulum. These clocks were much more accurate than previous
  clocks, off by less than a minute a day, compared to the 15
  minutes a day of earlier clocks. The bigger the pendulum, the
  more accurate the clock was.
  In 1714, the British Parliament
  offered a cash reward to anyone who could invent a clock accurate
  enough for use in navigation at sea. Thousands of sailors died
  because they were unable to find their exact position, because
  the exact time was needed to find longitude, and pendulum clocks
  would not work at sea. For every minute lost by a clock, it
  meant that there would be a navigational error of 15 miles,
  and sailors died because they were lost or smashed against rocks
  because they were unable to figure out their exact position.
  Then, in 1761, after 4 attempts, John Harrison finally succeeded
  at inventing a small clock accurate enough to use for navigation
  at sea. This tiny pocket watch lost only 5 seconds in 6 and
  In the early 1800’s,
  one of the most important events in clock making occurred. Eli
  Terry developed machines, patterns, and techniques that produced
  clock parts that were exactly alike, so they could be mass-produced
  and interchanged from one clock to another. This drove the price
  of clocks way down, and allowed common people to own at least
  one, if not many, timekeeping devices.
  At the dawn of the 20th century,
  only women wore wristwatches. No self-respecting "real
  man" would wear one. However, in the first World War, soldiers
  wore wristwatches because taking out a pocket watch to check
  the time was difficult or impossible in battle. After the war
  was over, it was considered "socially acceptable"
  to wear wrist watches, and they became popular. Half a century
  later, digital watches, which used electrical currents running
  through quartz crystals to cause vibration and tell the time
  very accurately, began to appear.
  The next great advancement
  in timekeeping was in 1967, when the atomic clock, which used
  the oscillations of cesium-133 atoms to tell time, was invented.
  This clock had an error ratio of 1 second for every 1.4 million
  years. Recently, in 1999, scientists developed the cesium fountain
  atomic clock, which is off by only one second every 20 million
  years. This clock is the most accurate in the world.