How does the imperium's date system work?

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**Cave_Dweller**

Been reading lots of fluff lately and I can't figure out what something like 846308.M41 means. I thought the first 3 digits meant the number of days counted in a year, and the last 3 meant the count of years in the millennium, but I don't think that's right. Anyone know? I'm dying to fill my brain with more completely useless information!

**SagesStone**

Check Number/Year Fraction/Year/Millennium.

The first is the reliability of the date by stating its position from Terra.

Class: 0/1 - Earth Standard Date. Referring to an event which happened within the Sol System. "0" is most commonly used to refer to an event which actually occured on Terra, while "1" refers to an event that occurred somewhere within the Sol System, such as Titan, the moon of the gas giant Saturn that serves as the headquarters of the Grey Knights Space Marines.
Class: 2 - Direct. The source for the event the date records was in direct psychic contact with the Sol System or Terra when the date reference was made.
Class: 3 - Indirect. The source for the event the date records was in direct contact with a Class 2 source, though not the Sol System itself.
Class: 4 - Corroborated. The source for the event the date records was in contact with a Class 3 source.
Class: 5 - Sub-Corroborated. The source for the event the date records is in direct psychic contact with a corroborated source.
Class: 6 - Non-Referenced, 1 year. The source for the event the date records is not in contact with a Class 0 to 5 source when the date reference was made, though it is a continuation of a timeline referenced by a Class 0 to 5 source.
Class: 7 - Non-Referenced, 10 years. As with Class 6 sources, but with a greater time span to allow for larger inaccuracies.
Class: 8 - Non-Referenced, 11+ years. As Class 7, though unsourced for a longer period of time.
Class: 9 - Approximation. For when worlds using a non-Imperial calendar must reference an event in that world's history.

The year is broken up into 1000 parts and the year then millennium is shown after it. But, it seems common to just have the year and millennium shown.

http://wh40k.lexicanum.com/wiki/Imperial_Dating_System#.Tx4pTaWO12A

**Vice_Grip**

It doesn't.

jk

**Cave_Dweller**

Ok, that's complicated...

**Ratius**

In your example there are only 6 digits so I think the check number has been excluded. Im assuming the check number is the one missing since the fraction and year must have 3 digits running from 000-999.
Assuming this is so it would mean

846 - this is the year fraction, sort of meaningless and only used by administration for reference

308 - this is the actual year within that millenium

M41 - the current millenium.

**CalgarsPimpHand**

The year fraction isn't meaningless at all. It gives the date and even the approximate time of day on Terra. 846 is 0.846*365, or 308.79, which works out to be something like 7 PM on November 4th (correct me if I'm wrong).

Breaking it up into a metric system of 000-999 makes sense when you have worlds that have completely different day lengths or days per year. No sense trying to reference the Terran calendar when the changeover of days and months is meaningless on your distant world.

Edit: Corrected myself, I was wrong

**Ratius**

The year fraction isn't meaningless at all. It gives the date and even the approximate time of day on Terra. 846 is 0.846*365, or 308.79, which works out to be something like 7 PM on November 4th (correct me if I'm wrong).

Got a source for that, news to me, although Im not saying its wrong.

**CalgarsPimpHand**

I don't think there's any source that works out the math like I did, but they say it's a decimal date, so I guess it's kind of implied? The year is broken up into 1000 parts, 000 through 999. So you should be able to work out what part of the year it is by multiplying the decimal by 365. Somebody please correct me if I'm wrong though, or source it if you know the source. I can't remember.

**Harriticus**

I really just pay attention to the last 3 numbers, the rest is too complicated and not that important. 2012 is 012.M3 for instance. That part is fairly easy.

**GCMandrake**

http://wh40k.lexicanum.com/wiki/Imperial_Dating_System

Pretty much:

0123456.M78

Where:

0 is the Check number (often omitted)
123 is the fraction of the year (from 000 to 999)
456 is the year of the millennium (000 to 999)
78 is the current millennium.

So today's date would be:

0063012.M3

**Grey Templar**

The 1000 parts of a year each correspond to roughly 8.76 hours. Days don't exist in the Imperial Calander because that is based on the orbit of the earth around the sun, but this is only for administratum purposes.

The Imperial Calander actually isn't a bad system for what it is used for. Quite handy actually.