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Decimal Time - Calendars

There have been many efforts to reform the Gregorian calendar. The Gregorian calendar itself was a 1582 reform of the Julian Calendar, which was in turn a reform of the Roman Replublican calendar by Julius Caesar in 45 BCE. Many other types of calendars have been used around the world and some are still in use. The primary obsticles to calendar reform are that religion and custom favor the existing calendar, and that incompatible cycles, such as days, weeks, months, seasons and years, are very difficult to rationalize with each other. Many calendar systems are based on the phases of the moon, which do not go evenly into a solar year, but the Julian, Gregorian and most of their derivative calendars are based on the seasons of the year, and have months of arbitrary lengths, usually 12. Since 365 days cannot be evenly divided by 12 or 10, the five odd days must be distributed in some way. Then there is slightly less than a quarter-day left over, which requires that additional days must be added every few years to keep the seasons from moving. It is not possible to reconcile more than one of these cycles with a completely decimal system, but there have been proposals for 10-day weeks or 10-month years.

French Republican Calendar

The French Republican Calendar was used in France and countries controlled by France from 1793 to 1805. This calendar was very similar to the ancient Egyptian and Alexandrian calendars, which are still used in Ethiopia and by the Coptic Church. Not only did the Republican Calendar include a decimal week, but also decimal time. Months of the Republican Calendar were divided into three décades, of ten days each. There were twelve 30-day months in a year, plus five or six complementary days at the end. Years began on the autumnal equinox, the Year One being counted retroactively from September 22, 1792, the first year of the Republic. Years were written in Roman numerals, following "l'Année", "An" or "l'An", meaning "year", or "ER" for "Era Républican". Décades of the month were also written in Roman numerals, I, II or III. An example date is "Décade III, Sextidi de Floréal de l'Année VIII de la Révolution", which could also be written as "26 Floréal, an VIII", or "VIII/8/26" for short, which was May 16, 1800 CE. There was a "rural" version, in which each day of the year also had its own name (just as the Catholic Church named days after saints in its calendar) the fifth day of the décade being named after an animal, the tenth day after a farm implement, and the rest after plants or minerals. The ten-day décades were very unpopular due to the division of the workweek and the conflict with Sundays, and stopped being used in Floréal an X (April 1802). The entire calendar was abandoned after Napolean became emperor, at the end of 1805.


The ten days of each décade were called:
Day Name Meaning Day Name Meaning
1 Primidi First Day 6 Sextidi Sixth Day
2 Duodi Second Day 7 Septidi Seventh Day
3 Tridi Third Day 8 Octidi Eight Day
4 Quartidi Fourth Day 9 Nonidi Ninth Day
5 Quintidi Fifth Day 10 Decadi Tenth Day


The months are shown below. Starting dates are approximate, and may fall one or two days later in some years.
Autumn Spring
Month Starts Name Meaning Month Starts Name Meaning
1 Sep 22 Vendémiaire Vintage 7 Mar 21 Germinal Germination
2 Oct 22 Brumaire Fog 8 Apr 20 Floréal Flowers
3 Nov 21 Frimaire Frost 9 May 20 Prairial Prairies
Winter Summer
Month Starts Name Meaning Month Starts Name Meaning
4 Dec 21 Nivôse Snow 10 Jun 19 Messidor Harvest
5 Jan 20 Pluviôse Rain 11 Jul 19 Thermidor Heat
6 Feb 19 Ventôse Wind 12 Aug 18 Fructidor Fruits

Complementary Days

The five or six days (depending on leap years) added to the end of the year were called Sansculotides or jours complémentaires (complementary days). There were several different naming conventions, including the following:
Day Name Meaning
1 Jour de la vertu Virtue Day
2 Jour du génie Genius Day
3 Jour du travail Labour Day
4 Jour de l'opinion Reason Day
5 Jour des récompenses Rewards Day
6 Jour de la révolution Revolution Day

Leap Years

Leap years, called sextile because they contained a sixth complementary day, occurred whenever two consecutive autumnal equinoxes happened to fall 366 days apart, as observed in Paris, which happened in the years III, VII and XI. A period of four years, at the end of which the addition of one day was necessary, was called a franciade, However, had the calendar continued in use, there would have been five years between the leap years XV and XX. There was also a problem that when the equinox occurred close to midnight, the margin for error made it impossible to predict whether it would fall on the day before or after midnight.

In the year III Gilbert Romme proposed rules similar to those of the Gregorian calendar, so that years divisible by 4 would be leap years, unless they were divisible by 100 and not divisible by 400. Also, the year 4000 would not be a leap year. However, he was sentenced to the guillotine and committed suicide shortly after, and the original equinox rule was followed, instead, with the first leap day occurring three months after his death. This method has the benefit that Republican years start on the same day in the Gregorian calendar for long periods; for instance, all years start on September 22 between 1993 and 2092.

Some concordances printed in France after 1805 continued having every four years after year 11 be leap years, i.e. 15, 19, 23, 27, 31, etc. Some in France today also calculate leap years this way, applying Romme's reformed rules to the year previous to what it would have been, so that the extra day is inserted immediately before most years divisible by four instead of added to the end. Thus, every four years since year 3 was a leap year, except years 99 and 199.

There are some who use a rule that from the year 20 on, years divisible by 4 are leap years, unless they are also divisible by 128. There seems to be no historical precedent for this rule.

Converting to Gregorian Calendar

The following table displays dates according to the Common Era for the first day of several years of the Republican Era, according to four methods of determining leap years:
  • Original rule: years start on equinox
  • Romme's revised rule: leap day added at end of years divisible by four, except centuries
  • Continuous rule: leap day inserted before years divisible by four, except centuries
  • 128-year rule: leap day added at end of years divisible by four, unless divisible by 128

RE CE Equinox Romme Continuous 128-Year

CCXV (215)


September 23*

September 22

September 22

September 23

CCXVI (216)


September 23

September 22

September 23*

September 23

CCXVII (217)


September 22

September 22*

September 22

September 23*



September 22

September 22

September 22

September 23

CCXIX (219)


September 23*

September 22

September 22

September 23

* Follows leap day at end of previous year

The New Digital Standard Calendar (NDSC)

According to The Digital Time web site:

This calendar contains 10 months with 10 days each. Therefore, a year lasts 100 days. At present, the calendar is synchronized so that the 01/01/2000 (old time) precisely coincides with the 0/0/2000 NDSC. There is no more "week;" a week is replaced by a month.
The New Digital Standard Time (NDST) is French decimal time, synchronized with UTC. NDSC months are numbered 0-9 and named Nuller, Prier, Secter, Trier, Quattrer, Penter, Sexter, Septer, Octer and Noner. The days of the month are likewise numbered 0-9, and are named Yourday, Myday, Momday, Dadday, Poorday, Giveday, Getday, Workday, Loveday, Restday.

William Gatchel's Standard/Metric Calendar

This Standard/Metric Calendar is actually the Gregorian calendar with 10-day weeks, plus French decimal time.

10 days = 1 metric week
36.5 metric weeks = 1 year
Months have the same names and lengths as Gregorian

Richard Ortiz's Metric Calendar

According to Richard Ortiz's web page:

In tune with revamping the entire chronological system, the New Year date/time is set to correspond to the Summer Solstice - Old June 21. This adds to the cosmological wholeness of the scheme in that the Metric New Year coincides with Natures New Year.

Next, of the twelve months in the old calendar, only the last 4 actually have names that describe their place in the year, ie, September is the seventh month, October is the eighth month, etc, so these were kept in their "original" positions. The beginning months simply run in order from January until they reach the last original 4, which naturally cuts out July and August.

Finally, The traditional days of the week are too much rabble to deal with on this kind of scale, and they are easily replaced with the names of celestial bodies in our solar system - 10 days:10 bodies.

A GigaTick would equal 365.2422 standard days.

A year would consist of 1000 MegaTicks:

  • 1 month = 100 MegaTicks giving us 10 months/yr.
  • 1 week = 10 MegaTicks giving us 10 weeks/month.
  • 1 day = 1 MegaTick.
    Hence a metric year has a thousand days.

  • Hal Mann's Decimal Calendar

    According to Hal Mann's web page:

    I propose that the calendar be divided into 10 months, instead of 12. Each month would be either 36 or 37 days long. Odd-numbered months would be 37 days long, and even-numbered months would be 36 days long. In leap years, the extra day would remain tacked on to the end of February (to keep from mucking up fixed-date holidays), becoming February 37th... In order to have only 10 months, I did away with June and July.

    Annus Novus Decimal Calendar

    The Annus Novus Decimal Calendar System is the calendar of the Empire of Atlantium, which claims to be an independent "microstate" within the city of Sydney, Australia.

    The Annus Novus year is of the standard terrestrial duration. The Annus Novus Calendar divides the year into 10 months alternating between 36 and 37 days in length, and 73 weeks of 5 days. In leap years - which are concurrent with those of the Gregorian system, to aid simplicity - an intercalary 1-day month called the Intercalarius is inserted between the last day of the old year and the start of the new year.
    The months have names derived from Latin: Primus, Secundus, Tertius, Quartarius, Quintus, Sextarius, Septimus, Octavus, Nonus and Decimus. The odd-numbered months have 36 days and the even-numbered ones have 37. The weekday names are similar to the first five days French Republican Calendar's décade: Primidi, Secundi, Tertidi, Quartidi and Quintidi. Years are numbered from the end of the Pleistocene Era, about 8520 BCE, so 2001 CE is 10520 "of the New Era". The first day of the year (1 Primidi) is always on January 1 on the Gregorian calendar.
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