Decimal time is the representation of the time of day using units which are decimally related. This term is often used specifically to refer to the time system used in France for a few years beginning in 1792 during the French Revolution, which divided the day into 10 decimal hours, each decimal hour into 100 decimal minutes and each decimal minute into 100 decimal seconds, as opposed to the more familiar UTC time standard, which divides the day into 24 hours, each hour into 60 minutes and each minute into 60 seconds.
The main advantage of a decimal time system is that, since the base used to divide the time is the same as the one used to represent it, the whole time representation can be handled as a single string. Therefore, it becomes simpler to interpret a timestamp and to perform conversions. For instance, 1:23:00 is 1 decimal hour and 23 decimal minutes, or 1.23 hours, or 123 minutes; 3 hours is 300 minutes or 30,000 seconds. This property also makes it straightforward to represent a timestamp as a fractional day, so that 20190521.534 can be interpreted as five decimal hours and 34 decimal minutes after the start of that day, or 0.534 (53.4%) through that day. It also adjusts well to digital time representation using epochs, in that the internal time representation can be used directly both for computation and for userfacing display.
GMT at page generation ()  

24h time  Decimal time 
13:35:24  5:66:25 
5h 66m 25s  
0.56625d 
Decimal time was used in China throughout most of its history alongside duodecimal time. The midnighttomidnight day was divided both into 12 double hours (traditional Chinese: 時辰; simplified Chinese: 时辰; pinyin: shí chén) and also into 10 shi / 100 ke (Chinese: 刻; pinyin: kè) by the 1st millennium BC.^{[1]}^{[2]} Other numbers of ke per day were used during three short periods: 120 ke from 5–3 BC, 96 ke from 507–544 CE, and 108 ke from 544–565. Several of the roughly 50 Chinese calendars also divided each ke into 100 fen, although others divided each ke into 60 fen. In 1280, the Shoushi (Season Granting) calendar further subdivided each fen into 100 miao, creating a complete decimal time system of 100 ke, 100 fen and 100 miao.^{[3]} Chinese decimal time ceased to be used in 1645 when the Shixian (Constant Conformity) calendar, based on European astronomy and brought to China by the Jesuits, adopted 96 ke per day alongside 12 double hours, making each ke exactly onequarter hour.^{[4]}
In 1754, Jean le Rond d'Alembert wrote in the Encyclopédie:
In 1788, Claude Boniface Collignon proposed dividing the day into 10 hours or 1000 minutes, each new hour into 100 minutes, each new minute into 1000 seconds, and each new second into 1000 tierces (Latin for "third"). The distance the twilight zone travels in one such tierce at the equator, which would be onebillionth of the circumference of the earth, would be a new unit of length, provisionally called a halfhandbreadth, equal to four modern centimetres. Further, the new tierce would be divided into 1000 quatierces, which he called "microscopic points of time". He also suggested a week of 10 days and dividing the year into 10 "solar months".^{[7]}
Decimal time was officially introduced during the French Revolution. JeanCharles de Borda made a proposal for decimal time on November 5, 1792. The National Convention issued a decree on 5 October 1793:
These parts were named on 24 November 1793 (4 Frimaire of the Year II). The primary divisions were called hours, and they added:
Thus, midnight was called either dix heures ("ten hours") or zero heures, noon was called cinq heures, etc. Units were either written out or abbreviated, such as 8 h. 72 m. Sometimes in official records, decimal hours were divided into tenths, or décimes, instead of minutes (e.g., 8.7 h.).^{[8]}^{[9]} Although clocks and watches were produced with faces showing both standard time with numbers 1–24 and decimal time with numbers 1–10, decimal time never caught on; it was not officially used until the beginning of the Republican year III, 22 September 1794, and mandatory use was suspended 7 April 1795 (18 Germinal of the Year III), in the same law which introduced the original metric system. Thus, although decimal time is sometimes referred to as metric time, the metric system at first had no time unit, and later versions of the metric system used the second, equal to 1/86400 day, as the metric time unit. In spite of this, decimal time was used in many cities, including Marseille and Toulouse, where a decimal clock with just an hour hand was on the front of the Capitole for five years.^{[8]} On the Palace of the Tuileries in Paris, two of the four clock faces displayed decimal time until at least 1801.^{[10]} The mathematician and astronomer PierreSimon Laplace had a decimal watch made for him, and used decimal time in his work, in the form of fractional days. Because of this, astronomers still use decimal time.
Decimal time was part of a larger attempt at decimalisation in revolutionary France (which also included decimalisation of currency and metrication) and was introduced as part of the French Republican Calendar, which, in addition to decimally dividing the day, divided the month into three décades of 10 days each; this calendar was abolished at the end of 1805. The start of each year was determined according to the day of the autumnal equinox, in relation to true or apparent solar time at the Paris Observatory. Decimal time would also have been reckoned according to apparent solar time, depending on the location it was observed, as was already the practice generally for the setting of clocks. 13:35:24 GMT is 5h 72m 74s decimal time in Paris.
At the International Meridian Conference of 1884, the following resolution was proposed by the French delegation and passed nem con (with 3 abstentions):
In the 1890s, Joseph Charles François de ReyPailhade, president of the Toulouse Geographical Society, proposed dividing the day into 100 parts, called cés, equal to 14.4 standard minutes, and each divided into 10 decicés, 100 centicés, etc. The Toulouse Chamber of Commerce adopted a resolution supporting his proposal in April 1897. Although widely published, the proposal received little backing.^{[11]}
The French made another attempt at the decimalization of time in 1897, when the Commission de décimalisation du temps was created by the Bureau des Longitudes, with the mathematician Henri Poincaré as secretary. The commission adopted a compromise, originally proposed by Henri de Sarrauton of the Oran Geographical Society, of retaining the 24hour day, but dividing each hour into 100 decimal minutes, and each minute into 100 seconds. The plan did not gain acceptance and was abandoned in 1900.
On 23 October 1998, the Swiss watch company Swatch introduced a decimal time called Internet Time, which divides the day into 1,000 decimal minutes (Swatch called them .beats), (each 86.4 seconds in standard time) counted from 000–999, with @000 being midnight and @500 being noon standard time in Switzerland, which is Central European Time (one hour ahead of Universal Time). A line painted on Swatch headquarters in the Swiss city of Biel (now Biel/Bienne) was declared to mark the Biel Meridian, and Central European Time was relabelled as "Biel Meantime" (BMT), even though it does not correspond to actual local mean time in Biel.^{[12]}
There are exactly 86,400 standard seconds (see SI for the current definition of the standard second) in a standard day, but in the French decimal time system there were 100,000 decimal seconds in the day, so the decimal second was shorter than its counterpart.
Decimal unit  Seconds  Minutes  Hours  h:mm:ss.sss 

Decimal second  0.864  0.0144  0.00024  0:00:00.864 
Decimal minute  86.4  1.44  0.024  0:01:26.400 
Decimal hour  8,640  144  2.4  2:24:00.000 
Another common type of decimal time is decimal hours. In 1896, Henri de Sarrauton of the Oran Geographical Society proposed dividing the 24 hours of the day each into 100 decimal minutes, and each minute into 100 decimal seconds.^{[13]} Although endorsed by the Bureau des Longitudes, this proposal failed, but using decimal fractions of an hour to represent the time of day instead of minutes has become common.
Decimal hours are frequently used in accounting for payrolls and hourly billing. Time clocks typically record the time of day in tenths or hundredths of an hour. For instance, 08:30 would be recorded as 08.50. This is intended to make accounting easier by eliminating the need to convert between minutes and hours.
For aviation purposes, where it is common to add times in an already complicated environment, time tracking is simplified by recording decimal fractions of hours. For instance, instead of adding 1:36 to 2:36, getting 3:72 and converting it to 4:12, one would add 1.6 to 2.6 and get 4.2 hours.^{[14]}
The time of day is sometimes represented as a decimal fraction of a day in science and computers. Standard 24hour time is converted into a fractional day by dividing the number of hours elapsed since midnight by 24 to make a decimal fraction. Thus, midnight is 0.0 day, noon is 0.5 d, etc., which can be added to any type of date, including (all of which refer to the same moment):
As many decimal places may be used as required for precision, so 0.5 d = 0.500000 d. Fractional days are often calculated in UTC or TT, although Julian Dates use pre1925 astronomical date/time (each date began at noon = ".0") and Microsoft Excel uses the local time zone of the computer. Using fractional days reduces the number of units in time calculations from four (days, hours, minutes, seconds) to just one (days).
Fractional days are often used by astronomers to record observations, and were expressed in relation to Paris Mean Time by the 18th century French mathematician and astronomer PierreSimon Laplace, as in these examples:^{[15]}
... et la distance périhélie, égale à 1,053095 ; ce qui a donné pour l'instant du passage au périhélie, sept.29^{j},10239, temps moyen compté de minuit à Paris. Les valeurs précédentes de a, b, h, l, relatives à trois observations, ont donné la distance périhélie égale à 1,053650; et pour l'instant du passage, sept.29^{j},04587; ce qui diffère peu des résultats fondés sur cinq observations.
— PierreSimon Laplace, Traité de Mécanique Céleste
Fractional days have been used by astronomers ever since. For instance, the 19th century British astronomer John Herschel gave these examples:^{[16]}
Between Greenwich noon of the 22d and 23d of March, 1829, the 1828th equinoctial year terminates, and the 1829th commences. This happens at 0^{d}·286003, or at 6^{h} 51^{m} 50^{s}·66 Greenwich Mean Time ... For example, at 12^{h} 0^{m} 0^{s} Greenwich Mean Time, or 0^{d}·500000...
— John Herschel, Outlines of Astronomy
Fractional days are commonly used to express epochs of orbital elements. The decimal fraction is usually added to the calendar date or Julian day for natural objects, or to the ordinal date for artificial satellites in twoline elements.
The second is the International System of Units (SI) unit of time duration. It is also the standard singleunit time representation in many programming languages, most notably C, and part of UNIX/POSIX standards used by Linux, Mac OS X, etc.; to convert fractional days to fractional seconds, multiply the number by 86400. Fractional seconds are represented as milliseconds (ms), microseconds (μs) or nanoseconds (ns). Absolute times are usually represented relative to 1 January 1970, at midnight. Other systems may use a different zero point (like Unix time).
In principle, time spans greater than one second are given in units such as kiloseconds (ks), myriasecond (mys), megaseconds (Ms), gigaseconds (Gs), and so on. (The myriasecond is based on the myria prefix, which represented a multiple of 10000 but was made obsolete in the mid20th century.) Occasionally, these units can be found in technical literature, but traditional units like minutes, hours, days and years are much more common, and are accepted for use with SI.
It is possible to specify the time of day as the number of kiloseconds or myriaseconds elapsed since midnight. Thus, instead of saying 3:45 p.m. one could say (time of day) 56.7 ks. There are exactly 86.4 ks or 8.64 mys in one day. However, this nomenclature is rarely used in practice.
Scientists often record (rather than observe) time as decimals. For example, decimal days divides the day into 10 equal parts, and decimal years divides the year into 10 equal parts. Decimals are easier to plot than both (a) minutes and seconds, which uses the Sexagesimal numbering system, (b) hours, months and days, which has irregular month lengths. In astronomy, the socalled Julian day uses decimal days centered on noon.
Since there are 60 seconds in a minute, a tenth part represents 60/10 = 6 seconds.
Decimal minutes  0.1  0.2  0.3  0.4  0.5  0.6  0.7  0.8  0.9  1.0 

Second  6s  12s  18s  24s  30s  36s  42s  48s  54s  60s 
Since there are 60 minutes in an hour, a tenth part represents 60/10 = 6 minutes.
Decimal hours  0.1  0.2  0.3  0.4  0.5  0.6  0.7  0.8  0.9  1.0 

Minutes  6m  12m  18m  24m  30m  36m  42m  48m  54m  60m 
Since there are 24 hours in a day, a tenth part represents 24/10 = 2.4 hours (2 hours and 24 minutes).
Decimal days  0.1  0.2  0.3  0.4  0.5  0.6  0.7  0.8  0.9  1.0 

Hours/minutes  2h 24m  4h 48m  7h 12m  9h 36m  12h  14h 24m  16h 48m  19h 12m  21h 36m  24h 
Since there are about 365 days in a year, there are about 365/10 = 36.5 days in a tenth of a year. Hence the year 2000.5 represents the day 2 July 2000.^{[17]} More exactly, a Julian year is exactly 365.25 days long, so a tenth of the year is 36.525 days (36 days, 12 hours, 36 minutes).
Decimal years  0.0  0.1  0.2  0.3  0.4  0.5  0.6  0.7  0.8  0.9  1.0 

Days  0  36.525  73.050  109.575  146.100  182.625  219.150  255.675  292.200  328.725  365.250 
Date Time 
1 Jan 0:00 
6 Feb 12:36 
15 Mar 1:12 
20 Apr 13:48 
27 May 2:24 
2 Jul 15:00 
8 Aug 3:36 
13 Sep 16:12 
20 Oct 4:48 
25 Nov 17:24 
1 Jan 6:00 
These values, based on the Julian year, are most likely to be those used in astronomy and related sciences. A Gregorian year, which takes into account the 100/400 leap year rules of the Gregorian calendar, is 365.2425 days (the average length of a year over a 400year cycle), resulting in 0.1 years being a period of 36.52425 days (3155695.2 seconds; 36 days, 12 hours, 34 minutes, 55.2 seconds).
Numerous individuals have proposed variations of decimal time, dividing the day into different numbers of units and subunits with different names. Most are based upon fractional days, so that one decimal time format may be easily converted into another, such that all the following are equivalent:
Some decimal time proposals are based upon alternate units of metric time. The difference between metric time and decimal time is that metric time defines units for measuring time interval, as measured with a stopwatch, and decimal time defines the time of day, as measured by a clock. Just as standard time uses the metric time unit of the second as its basis, proposed decimal time scales may use alternative metric units.
The 12hour clock is a time convention in which the 24 hours of the day are divided into two periods: a.m. (from Latin ante meridiem, translates to, before midday) and p.m. (from Latin post meridiem translates to, past midday). Each period consists of 12 hours numbered: 12 (acting as zero), 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, and 11. The 24 hour/day cycle starts at 12 midnight (may be indicated as 12 a.m.), runs through 12 noon (may be indicated as 12 p.m.), and continues to the midnight at the end of the day. The 12hour clock has been developed from the middle of the second millennium BC to the 16th century AD.
The 12hour time convention is common in several Englishspeaking nations and former British colonies, as well as a few other countries.
24hour clockThe 24hour clock is the convention of time keeping in which the day runs from midnight to midnight and is divided into 24 hours, indicated by the hours passed since midnight, from 0 to 23. This system is the most commonly used time notation in the world today, and is used by international standard ISO 8601.A limited number of countries, particularly Englishspeaking, use the 12hour clock, or a mixture of the 24 and 12hour time systems. In countries where the 12hour clock is still dominant, some professions prefer to use the 24hour clock. For example, in the practice of medicine the 24hour clock is generally used in documentation of care as it prevents any ambiguity as to when events occurred in a patient's medical history. In the United States and a handful of other countries, it is popularly referred to as military time.
Blitz BASICBlitz BASIC refers to the programming language dialect that was interpreted by the first Blitz compilers, devised by New Zealandbased developer Mark Sibly. Being derived from BASIC, Blitz syntax was designed to be easy to pick up for beginners first learning to program. The languages are gameprogramming oriented but are often found generalpurpose enough to be used for most types of application. The Blitz language evolved as new products were released, with recent incarnations offering support for more advanced programming techniques such as objectorientation and multithreading. This led to the languages losing their BASIC moniker in later years.
Claude Boniface CollignonClaude Boniface Collignon (died 1819) was a French attorney who contributed to scientific and social reforms in the time of the French Revolution. He was a member of several European academies of sciences, though not the French Academy of Sciences. In 1788 he proposed the introduction of decimal time. In 1790, perhaps disappointed that the French government had not immediately rewarded him for the plan, he sent his book to George Washington, and proposed to introduce his system in the US.
Clock faceA clock face, or dial, is the part of an analog clock (or watch) that displays the time through the use of a fixednumbered dial or dials and moving hands. In its most basic form, recognized throughout the world, the periphery of the dial is numbered 1 through 12 indicating the hours in a 12hour cycle, and a short hour hand makes two revolutions in a day. A long minute hand makes one revolution every hour. The face may also include a second hand, which makes one revolution per minute. The term is less commonly used for the time display on digital clocks and watches.
A second type of clock face is the 24hour analog dial, widely used in military and other organizations that use 24hour time. This is similar to the 12hour dial above, except it has hours numbered 1–24 around the outside, and the hour hand makes only one revolution per day. Some specialpurpose clocks, such as timers and sporting event clocks, are designed for measuring periods less than one hour. Clocks can indicate the hour with Roman numerals or Hindu–Arabic numerals, or with nonnumeric indicator marks. The two numbering systems have also been used in combination, with the prior indicating the hour and the latter the minute. Longcase clocks (grandfather clocks) typically use Roman numerals for the hours. Clocks using only Arabic numerals first began to appear in the mid18th century.The clock face is so familiar that the numbers are often omitted and replaced with applied indices (undifferentiated hour marks), particularly in the case of watches. Occasionally, markings of any sort are dispensed with, and the time is read by the angles of the hands.
CollignonCollignon is a surname, and may refer to:
Charles Collignon, French fencer and 1908 Olympic champion
Christophe Collignon (b. 1969), Belgian politician
Claude Boniface Collignon (d. 1819), French proponent of decimal time and metric system
Édouard Collignon (1831–1913), French engineer and scientist
François Collignon (c. 16091687), French engraver
Frédéric Collignon (b. 1975), Belgian table football player
Jean Nicolas Collignon (1762–?1788), French botanist
Médéric Collignon (born 1970), French musician
Decimal calendarA decimal calendar is a calendar which includes units of time based on the decimal system. For example a "decimal month" would be , or 36.5 days long.
Decimalisation (disambiguation)Decimalisation or decimalization is the conversion of a measurement system to units of decimal (base ten) form, instead of traditional units of other forms, such as those formed by successive doubling or halving. For example, a series of (1000, 100, 10, 1, 0.1, 0.01, 0.001) instead of (16, 8, 4, 2, 1, 1⁄2, 1⁄4, 1⁄8, 1⁄16, 1⁄32, 1⁄64). Thus the word may refer to:
Decimalisation of currencies
Decimalisation of physical measurements (such as distance or weight), intimately bound historically with metrication
Decimalisation of time units
Decimalisation of the time of day via decimal time systems
Decimalisation of the calendar via decimal calendar systems
French Republican calendarThe French Republican calendar (French: calendrier républicain français), also commonly called the French Revolutionary calendar (calendrier révolutionnaire français), was a calendar created and implemented during the French Revolution, and used by the French government for about 12 years from late 1793 to 1805, and for 18 days by the Paris Commune in 1871. The revolutionary system was designed in part to remove all religious and royalist influences from the calendar, and was part of a larger attempt at decimalisation in France (which also included decimal time of day, decimalisation of currency, and metrication). It was used in government records in France and other areas under French rule, including Belgium, Luxembourg, and parts of the Netherlands, Germany, Switzerland, Malta, and Italy.
Hexadecimal timeHexadecimal time is the representation of the time of day as a hexadecimal number in the interval [0,1).
The day is divided into 1016 (1610) hexadecimal hours, each hour into 10016 (25610) hexadecimal minutes, and each minute into 1016 (1610) hexadecimal seconds.
Julian dayJulian day is the continuous count of days since the beginning of the Julian Period and is used primarily by astronomers, and in software for easily calculating elapsed days between two events (e.g. food production date and sell by date).
The Julian Day Number (JDN) is the integer assigned to a whole solar day in the Julian day count starting from noon Universal time, with Julian day number 0 assigned to the day starting at noon on Monday, January 1, 4713 BC, proleptic Julian calendar (November 24, 4714 BC, in the proleptic Gregorian calendar), a date at which three multiyear cycles started (which are: Indiction, Solar, and Lunar cycles) and which preceded any dates in recorded history. For example, the Julian day number for the day starting at 12:00 UT on January 1, 2000, was 2 451 545.The Julian date (JD) of any instant is the Julian day number plus the fraction of a day since the preceding noon in Universal Time. Julian dates are expressed as a Julian day number with a decimal fraction added. For example, the Julian Date for 00:30:00.0 UT January 1, 2013, is 2 456 293.520 833.The Julian Period is a chronological interval of 7980 years; year 1 of the Julian Period was 4713 BC. It has been used by historians since its introduction in 1583 to convert between different calendars. The Julian calendar year 2019 is year 6732 of the current Julian Period. The next Julian Period begins in the year AD 3268.
List of unusual units of measurementAn unusual unit of measurement is a unit of measurement that does not form part of a coherent system of measurement; especially in that its exact quantity may not be well known or that it may be an inconvenient multiple or fraction of base units in such systems.
This definition is not exact since it includes units such as the week or the lightyear are quite "usual" in the sense that they are often used but which can be "unusual" if taken out of their common context, as demonstrated by the Furlong/Firkin/Fortnight (FFF) system of units.
Many of the unusual units of measurements listed here are colloquial measurements, units devised to compare a measurement to common and familiar objects.
Metric timeMetric time is the measure of time intervals using the metric system. The modern SI system defines the second as the base unit of time, and forms multiples and submultiples with metric prefixes such as kiloseconds and milliseconds. Other units of time: minute, hour, and day, are accepted for use with SI, but are not part of it. Metric time is used for time intervals, while decimal time is used for time of day.
New Earth TimeNew Earth Time (or NET) is an alternative naming system for measuring the time of day. In NET the day is split into 360 NET degrees, each NET degree is split into 60 NET minutes and each NET minute is split into 60 NET seconds. One NET degree is therefore equivalent to four standard minutes, and one standard hour is equivalent to 15 NET degrees.
NET is equivalent to the UTC read from a 24hour analog clock as the clockwise angle past midnight of the hour hand. For example, noon is 180°0'0" NET and at that time the hour hand is pointing straight down forming a 180° angle when measured from the top, at midnight. A full circle is 360 degrees and one NET day.
Swatch Internet TimeSwatch Internet Time (or .beat time) is a decimal time concept introduced in 1998 by the Swatch corporation as part of their marketing campaign for their line of "Beat" watches.
Instead of hours and minutes, the mean solar day is divided into 1000 parts called ".beats". Each .beat is equal to one decimal minute in the French Revolutionary decimal time system and lasts 1 minute and 26.4 seconds (86.4 seconds) in standard time. Times are notated as a 3digit number out of 1000 after midnight. So, @248 would indicate a time 248 .beats after midnight representing 248/1000 of a day, just over 5 hours and 57 minutes.
There are no time zones in Swatch Internet Time; instead, the new time scale of Biel Meantime (BMT) is used, based on Swatch's headquarters in Biel, Switzerland and equivalent to Central European Time, West Africa Time, and UTC+01. Unlike civil time in Switzerland and many other countries, Swatch Internet Time does not observe daylight saving time.
Traditional Chinese timekeepingThe traditional Chinese time systems refers to the time standards for divisions of the day used in China until the introduction of the Shixian calendar in 1628 at the beginning of the Qing dynasty.
Units of measurement in FranceFrance has a unique history of units of measurement due to the radical decision to invent and adopt the metric system after the French Revolution.
In the Ancien régime, before 1795, France used a system of measures that had many of the characteristics of the modern Imperial System of units. There was widespread abuse of the king's standards to the extent that the lieue could vary from 3.268 km in Beauce to 5.849 km in Provence. In the revolutionary era, France used the first version of the metric system. This system was not well received by the public. Between 1812 and 1837, the mesures usuelles was used – traditional names were restored, but were based on metric units: for example, the livre became 500 g. After 1837, the metric system was reintroduced and has remained the principal system of use to this day.
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