Synchronized with the northern winter solstice, the terran computational calendar began roughly^{[notes 1]} 10 days before the UNIX Epoch. Each year is composed of 13 identical 28-day months, followed by a 'minimonth' that houses leap days (one most years and two every 4th but not 128th year) and leap seconds (issued by the IERS during that year). Each date is an unambiguous instant in time that exploits zero-based numbering and a handful of delimiters to represent the number of years and constant length months, days, hours, minutes, and seconds that have elapsed since 0TC (the calendar's starting point). An optional 'year base' may be applied to ignore erratic leap duration. Arithmetic date adjusting datemods can be applied to define things like weeks, quarters, and regional times.^{[1]}

## Terran Computational Epoch[]

The epoch is roughly synchronized with the northern winter solstice, and the exact instant of this calendar's epoch is officially defined as 221788790 SI seconds (measured at the geoid) before 1977-01-01 00:00:00 TAI. Though for most practical purposes, it may be reasonable to use 1969-12-22 00:00:00 UTC or -864000 seconds of (10 days before) the UNIX Epoch as the terran computational epoch.
For the rationale, see the epoch section on the homepage^{[2]}

## Basic Time Measurement[]

### Years[]

__Date Field Range:__ Any integer value.
__Duration:__ 13 full terran computational months plus a given year's minimonth (which corresponds to that year's leap duration).

### Months & Minimonth[]

__Combined Date Field Range:__ 0-13

#### Months[]

__Date Field Range:__ 0-12
__Duration:__ 28 days

#### Minimonth[]

__Date Field Range:__ 13
__Duration:__ Equal to a given year's leap duration which includes the duration of all [[#Leap_Second|leap seconds], …, leap days, … in a given year.

### Days[]

__Date Field Range:__ 0-27
__Duration:__ 24 hours

### Hours[]

__Date Field Range:__ 0-23
__Duration:__ 60 minutes

### Minutes[]

__Date Field Range:__ 0-59
__Duration:__ 60 seconds

### Seconds[]

__Date Field Range:__ 0-59
__Duration:__ An SI second measured at mean sea level (Wikipedia:Geoid|the geoid]])

### Fractions of a Second[]

__Date Field Range:__ Any decimal value
__Duration:__ Any positive duration less than a single second.

## Dynamic Time Measurement[]

### Year Base[]

A year base is optional and is appended to the right hand side of the 'TC' in a given date's designator and together they effectively create their own distinct designator. A given year base, *n*, signifies that only erratic leap duration before *n*TC should be accounted for and any erratic leap duration after *n*TC will be ignored. The terran computational calendar does not account for erratic leap duration before 0TC, therefore, TC0 is a designator with a year base of 0 signifying that ALL erratic leap duration should be ignored. Negative year bases are not allowed and any attempt to do so would result in a datemod instead. If no year base is provided, all erratic leap duration will be accounted for.

#### Proactive Dating[]

'Year basing' is specifically useful when writing a date in the future where erratic leap duration is unknown.

### Datemod[]

The optional 'datemod' (which stands for 'date modification') field takes the place of traditional timezones and offsets by adding or subtracting to/from the date instant.

#### Datemod Values[]

A datemod with only an integer value and no letters indicates an integer number of seconds that the terran computational date should be modified by. The datemod field may alternatively represent the number of **M**inutes, **H**ours, **D**ays, **W**eeks, **L**unas (months), **Q**uarters if proceeded by a M, H, D, W, L, or Q respectively. Any combination may be used as well as long as they are in decreasing order of value, so for instance, 44.1.2.3.4.5TC could be written as 44TC+4W2D3H4M5 or 44TC+1L2D3H4M5. Notice that if a letter doesn't follow a number value, then it should be treated as seconds.

#### Timestamp[]

A terran computational timestamp begins with a "TC" designator proceeded by delimiter and a datemod indicating the number of continuous seconds that have past since the the terran computational epoch. The current timestamp at the time of this writing is TC+1402312636.

## Leap Duration[]

A terran computational year's leap duration is defined as the sum of all leap units (leap seconds,…, & leap days,…) within that year. This leap duration is put into an additional minimonth at the end of the year. All leap units have the same field placement within a date and are equal in duration to their corresponding unit.

### Leap Days[]

There is always at least 1 leap day per year. On years that are a multiple of 4 but not of 128, an additional leap day is included resulting in 2 leap days that year. Adding leap days in this fashion is extremely efficient and will keep each year synchronized with the northern winter solstice.

### Leap Seconds[]

Any leap seconds issued by the IERS within the bounds of a given terran computational year will manifest themselves in a year's minimonth. The terran computational calendar does not account for erratic leap duration before 0TC, so to ignore all leap seconds, apply a year base of 0 to a date's designator (TC0). There have been 25 leap seconds since 0TC, all of which occurred in different years (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 15, 18, 20, 21, 22, 23, 24, 26, 27, 29, 36, 39, 42).

### Erratic Leap Duration[]

Erratic leap duration refers to unknown or unstable leap duration, such as IERS issued leap seconds. No erratic leap duration occurs before 0TCm, so, to ignore all leap seconds, apply a year base of 0 to a date's designator (TC0).

## Date Notation[]

The following is equivalent to the terran computational epoch (0TC):

Each terran computational date defines an exact unambiguous instant in time and is composed of a designator plus other conditionally optional date fields concatenated together by conditionally optional delimiters. In order, these fields are year, month, day, hour, minute, second, fraction, designator, datemod and their ranges are roughly: ±*.[0-13].[0-27].[0-23].[0-59].[0-59].*.TC*±*, where * is any acceptable range. The a recent terran computational date (which could be written like this: 44.5.17,4.23.41 TC) literally means that exactly 44 years, 5 months, 17 days, 4 hours, 23 minutes, and 41 seconds have passed since the Terran Computational Epoch. To learn about the all the other acceptable ways to write terran computational dates, see the algorithm for formatting & parsing section^{[3]} of the homepage.

### Designator[]

'TC' is an acronym for 'terran computational'. Terran computational dates and written timestamps must utilize a 'TC' and optionally concatenated positive integer year base as a designator. A 'TC' designator without a year base signifies that all known erratic leap duration should be accounted for. A 'TC' designator with a given year base, *n*, signifies that only erratic leap duration before *n*TC should be accounted for.

### Delimiters[]

Delimiters separate date fields from one another. The only 8 acceptable delimiters are space, plus, comma, minus, dot, slash, colon and underscore ( +,-./:_) (UTF8 hex codes 20, 2b, 2c, 2d, 2e, 2f, 3a, 5f). A delimiter directly before the designator is optional. See the algorithm for formatting & parsing section^{[3]} on the homepage for exact rules.

## Accommodated Time Measurement[]

The following can be expressed, in some manner, utilizing datemods. Weeks and quarters can be expressed, in some manner, utilizing datemods and decades, centuries, & millennia are implied by years.

### Weeks[]

One week is defined as the duration of 7 days. Any integer number of weeks can be expressed by appending a W as a datemod. For example, 44TC+39W is the equivalent of 44.9.21TC, or if you want to do away with years, and use weeks for the highest unit, you could write this date as TC+2334W5D25

### Quarters[]

One quarter is defined as the duration of 13 weeks. Any integer number of quarters can be expressed by appending a Q as a datemod For example, 44TC+3Q is the equivalent of 44.9.21TC, or if you want to do away with years, and use quarters for the highest unit, you could write this date as TC+179Q7W5D25

### Decades, centuries, & millennia[]

Just like years, decades, centuries, and millennia also function as integers whereby decade -1 covers years -10 through -1 and decade 0 covers years 0 through 9; millennia -1 would cover years -1000 to -1 and millennia 0 would cover years 0 through 999.

## Unaccommodated Time Measurement[]

The following cycles have complex algorithms or are somewhat erratic and therefore the terran computational calendar has not hard-wired simple ways to track their cycles into its algorithm.

### Timezone Abbreviations[]

The terran computational calendar does not implement or support traditional timezone abbreviations, but it does allow for dynamic date modifications, or 'datemods' which easily represent regional time.

### Seasons, Solstices, & Equinoxes[]

While the terran computational calendar accommodates quarters, the only season/solstice that the terran computational calendar tracks, within some degree of extreme ease, is the beginning of winter and the winter solstice of the northern hemisphere which falls around the beginning/end of each year. But even that is not constant, so in order to determine the exact time of an equinox, solstice, or season, please consult some sort of table.

### Moon Cycles[]

The cycles of the moon, like most objects in our solar system including the earth, are somewhat erratic. And although months are a general approximation of lunar cycles, the terran computational calendar makes no attempt to track these cycles explicitly.

### Milankovitch Cycles[]

Milankovitch Cycles include the many cycles of the earth whose periods are on timescales of tens of thousands of years. Since these periods are so extensive and also so erratic, they are generally incredibly difficult to predict within any great degree of accuracy. Therefore, the terran computational calendar does not explicitly track any of these cycles.

## Accuracy, Neutrality, & Permanency[]

### Calendar Accuracy[]

Adding leaps days in years that are a multiple of 4 but not a multiple of 128 creates an extremely efficient time keeping method. Much more so than any other simplistic consistent algorithm.

### Neutrality[]

Apart from inherent bias, the terran computational calendar intends to be a non-biased neutral calendar for anyone to use for any purpose. Besides its connections to math, computers, atomic time, and astronomy, this calendar does not intend to favor any culture or creed, time, or place. It is a simple idea intending to remain as simple as possible for its purpose, nothing more. The terran computational public domain mark^{[4]} allows people to use the calendar without having worry about most legal restrictions.

### Level of Permanency[]

The terran computational calendar maintains a very high level of conformity and permanency:

- Each full month, day, hour, minute, second, week, and quarter are of constant length.
- Each time measurement unit begins at 0.
- Years, decades, centuries, etc. are integer based.
- Each year begins near the northern winter solstice.
- Each quarter lasts for 3¼ months or 13 weeks
- Calendrical drift is suspended by including leap days in years that are a multiple of 4 but not of 128
- All written dates are unambiguous.
- Any date tells you explicitly how many years, months, days, hours, minutes, and seconds have past since the terran computational epoch.

## Code & Downloads[]

The terran computational website offers code and downloads^{[5]} to implement and run the calendar.

## Notes[]

- ↑ TAI dates before 1977 are not defined in the way they are now, so conversions before 1977 may differ by up to a number of milliseconds.