Metric time
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Metric time is a system of time measurement, which uses a single base time unit along with multiple and submultiple [[metric [refixes]]; for example, a possible metric time measurement would use the units days, decidays, centidays, millidays, and microdays.
Several proposals for metric time systems not based on the second, but rather on decimal fractions of the mean solar day have been proposed. some of which are based on a unit of 10-5 days, which is 86.4 seconds. One metric time system, Sekants Time, is based on a unit of 10-6 mean solar days or one microday, and uses a revised metric prefix set. This form of metric time may also be called integer time.
The origins of metric time can be traced to France during the French Revolution, in the form of a French Revolutionary Decimal Clock, which was never officially adopted, and was rejected 2 years after its introduction. This prototype decimal time system was not a true example of metric time, since the original metric system did not include a base unit of time, and metric prefixes were only added to the metric system long after the decimal clock proposal had been abandoned. However later forms of decimal and metric time were no doubt inspired by the French model, which divided the day into decimal units in methods similar to the following:
- 10 decimal hours in a day (2 h 24 min each)
- 100 decimal minutes in a decimal hour (1 min 26.4 s each)
- 100 decimal seconds in a decimal minute (0.864 s each)
- 10 days in a metric week (called a dekade)
The metric system did not include a metric unit of time until nearly a century later, when Maxwell and Thomson (through the British Association for the Advancement of Science - BAAS) introduced the CGS (centimeter, gram, second) system in 1874, in order to derive electric and magnetic metric units, following the recommendation of Gauss in 1832.
The Astronomical second (defined as 1/86400 part of a Mean Solar Day) became the SI second with the introduction of the International System of Units at the 11th CGPM in 1960.
The SI later redefined the second as the duration of : 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom.
An example of metric time based on the SI second is UNIX time, which counts seconds as integers from 1 January 1970. This form integer time, which is not based on the mean solar day, is now refered to as Serial time.
One popular form of decimal time is Swatch Internet time, which divides the day into 1000 ".beats". Zero .beats, written @000, is aligned to midnight CET, (UTC+1), local time at Swatch Headquarters, in Biel Switzerland. Beat time, however, cannot be regarded as metric time, since it does not use metric multiple and submultiple prefixes, but rather Gregorian Dates + Fractional Days.
No country has officially adopted metric time. Given the complexity involved in a changeover from the current SI metric system in universal use, (with the exception of the USA which still uses former English Imperial unit system). Although one metric time system, Sekants Time, is actually part of a revised Pandecimal metric system, (proposed in Europe, in 1990), to replace the current SI system.
Metric time systems have sometimes been used in fictional settings. For example, in Vernor Vinge's science fiction novel, A Deepness in the Sky, the characters measure time with seconds, kiloseconds and megaseconds.