Imperial Calendar


		Imperial Calendar
		Since Rouge Trader, Warhammer 40K has used an arcane dating system.  
		I thought I'd do the obligatory explanation of horology in the 41st 
		millennium, and make sure people can figure out some of the weird dates.
		
		
			A typical date might be 4.423815.M41. This can be broken down into 4 
			basic parts- 4.  423   815  M41. 
		
			The first part is the check number, which determines the degree of 
			probable accuracy in the rest of the date: 
		
			a check number of 0 or 1 indicates the date refers to an event 
			occurring in the Sol system 
			
			 2 indicating a system in direct astropathic contact with Terra 
			
			 3 indicates the source was not in direct contact with Terra, 
			but was in contact with a class 2 source 
			
			In contact with a class 3, but not a class 0/1 or 2 
			
			In contact with a class 4 source 
			
			Was not in direct psychic contact with any other source at that 
			time, but the date is part of a sequence that begins or ends with a 
			source referenced date of class 1-5. The unreferenced period is no 
			greater than 1 standard year 
			
			As class 6, but the unreferenced period is between 1 and 10 
			standard years 
			
			A check number of 8 indicates that the unsourced period is 
			greater than 10 years 
			
			An approximated date- either this belongs to a date sequence 
			with no fixed co-ordinate at either end (such as a date given from 
			the Dark Age of Technology), or the date has been approximated from 
			a non-imperial dating system
		
		Obviously, check numbers of 0-5 are relatively accurate, while 6-8 
		represent a widening grey area of inaccuracy. Class 9 is somewhat 
		different, but can generally be assumed to be roughly accurate (maybe). 
		It is probably worth remembering that the period separating the check 
		number from the rest of the date is optional.
		
			The next portion of three digits (423 in this case) is the year 
			fraction. Each year is broken up into 1000 equal segments, numbered 
			000-999, for administrative purposes (I suspect; though not stated 
			in canonical fluff, but is fairly logical to assume; that these 
			'administrative purposes' are to make it easier to convert local 
			dates, it being simpler to convert something in relation to 1000 
			than to 365). 
			Assuming an Imperial standard year is based upon a Terran 
			sidereal year (not too unreasonable) that gives us a year fraction 
			(call it a 'watch') of just over 8hrs, 45 minutes and 57 seconds in 
			length. Perhaps not unsurprisingly, this portion is not really in 
			general use among Imperial citizens, although anyone who needs to 
			refer to and keep track of time on different planets will do so in 
			preference to local date systems. Our example date is sometime 
			between ~11:30 AM and ~8:15 PM on May 16th, therefore.
		
			 
		
			The next three digits are the year, going from 001 to 000 (one 
			thousand), so our example date is the eight hundred and fifteenth of 
			its millennium, which brings us neatly to the final portion of the 
			date, which is the millennium itself. m41 (or occasionally M41, or 
			just /41 or .41) is the forty first millennium, the 'current' period 
			of the game setting, meaning our example date (which, like all 
			general dates, may be abbreviated to the form 815.m41) is the 815th 
			year of the 41st millennium (or the year 40,815 CE). Incidentally, 
			this is the same year as the official setting for Dark Heresy RPG 
			and a lot of the GW fluff.
		
			 
		
			So, if we put this all together, what do we get? 4.423815.m41= 
			between 1130 and 2016 hrs on May 16th, in the year 40,815 AD, in a 
			system that was in contact with a system in contact with a system in 
			contact with Earth.