<Li> Greenwich Mean Time (or Coordinated Universal Time) is designated time zone Z, and thus called "Zulu time". </Li> <Li> Hours are always "hundred", never "thousand"; 1000 is "ten hundred" not "one thousand"; 2000 is "twenty hundred" not "two thousand". </Li> <P> The 24 - hour time system has its origins in the Egyptian astronomical system of decans, and has been used for centuries by scientists, astronomers, navigators, and horologists . In East Asia, time notation was 24 - hour before westernization in modern times . Western - made clocks were changed into 12 dual - hours style when they were shipped to China in the Qing dynasty . There are many surviving examples of clocks built using the 24 - hour system, including the famous Orloj in Prague, and the Shepherd Gate Clock at Greenwich . </P> <P> The first mechanical public clocks introduced in Italy were mechanical 24 - hour clocks which counted the 24 hours of the day from one half hour after sundown to the evening of the following day . The 24th hour was the last hour of day time . However, striking clocks had to produce 300 strokes each day which required a lot of rope, and wore out the mechanism quickly, so some localities switched to ringing sequences of 1 to 12 twice (156 strokes), or even 1 to 6 repeated 4 times (84 strokes). </P>

Where did the 24 hour clock come from
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