What is the "r" dating system that is connected to Byzantium?

I’d never seen or noticed this before I saw it in the Art Institute the other day. It was used to date some coins that were Byzantine. When I look on Wiki, I see it used, but I don’t really know what it is based on, when it supposedly began, etc. Historians, what’s the straight dope on this system? xo,
C.

Are you sure it is an R or is it an upper case Gamma Γ

Γ was a used for the officina or the mint that made the coin and think it will probably have “CON” on the coin for Constantinople.

Here is a link that should explain it.

http://www.forumancientcoins.com/numiswiki/view.asp?key=officina

Not exactly what I’m talking about. This is a small excerpt from Wikipedia:
“Constantine I (r. 324–337)”
It seems to be a numbering system akin to B.C. or A.D. or BCE. I just have never come across it before. It seems to refer only to Byzantine events.

That either stands for “rex” or “reigned”, and in any case indicates the range of dates in which he ruled the empire.

Yep - Wikipedia entries use ‘Reigned’ in the right hand side main entry block, but I’m sure you’ll find examples of ‘Ruled’, ‘Rex’ and ‘Ran the place’ if you look hard enough.

This may be a little late, but just to clarify - the regnal ® dates are not specific to Byzantine emperors. It is the most common way to show when a particular Emperor/King/Pope/whatever held the title. For instance, looking up James II of England might show up as: James II (r. 1685-1688). Even more likely IMHO it would be: James II (1633-1701, r 1685-1688). The first set of dates are birth and death, with the second set following the “r” showing the period that he was head honcho.