Well, the quick and dirty... (If you want exact formuae, consult the discussions forums) [Actually, strike "quick." I tend to over-explain...
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There are two numbers you seem to refer to, rank and ELO. These numbers are related, but are quite different. Rereading the original post, I think zdepthcharge used the word "rank" when discussing ELO.
ELO can be thought of as a probability of a person winning a particular game. If two players have the same ELO, they should each win half the time. It doesn't matter if they both have a high ELO (both experts) or both have a low ELO (both apprentices) -- their skill levels are the same, they are equally matched. However, when ELO is different, the player with the higher ELO should have a higher probability of winning. I think the numbers boil down to that if the difference in ELO is 100, the stronger player is expected to win 2 out of every 3 matches, and if the difference is 200, they are expected to win 3 out of every 4 matches. This leads to the titles "apprentice," "good," "expert," etc.
ELO was designed for chess, and adapted for many other games. With that, there are some issues. First, chess does not have a score: it is either a win or a loss (well, OK, it could also be a tie). With that, for games like Stone Age, it does not matter if the win is 50-1 or 101-100; both scores calculate as a win. Also note that chess is a strictly 2-player game. BGA has tweaked it so that in multi-player games, the calculation is done as if several simultaneous 2-player games were done at once. IE, if the final positions of the players were A, B, C, D, the ELO would be calculated as A wins against B,C,D -- B loses to A, but wins against C, D -- C looses to A and B, but wins against D, and D has 3 losses.
ELO, after several games, is a zero-sum point transfer. ELO gained by the winner is equal to ELO lost by the looser. But, again, this is after several games. While the system is trying to determine what a new player's true ELO is, it may give or remove more points with them.
Going back to the probability of winning, the point transfer is greater for a lower ELO to win against a higher ELO than for the higher ELO winning against a lower. IE, if someone who is expected to win 3 out of every 4 matches 3 of 4, it's not an accomplishment. But, if someone who is expected to win only 1 out of 4 wins 2 of 4, it is an accomplishment. (Fine, it really should be 30 out of 40 and 20 out of 40, but whatever...) This is why the 244 v 496 match transferred 4-5 points (rounding), while the 10-point difference match transferred 10 points.
Now, as to rank.
Rank is how a player's ELO measures against all other players' ELO on the site. The person with the highest ELO is ranked first, second highest ELO is ranked second, etc. Take all players with an ELO on this site, put them in a list, and sort by ELO -- you get the ranking. It doesn't matter if 20th place has an ELO 10 points or 30 points higher than 21st place, it is still 1 place higher.
Hope that helped.
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Edit -- the most effective search to find details is probably "k factor" or "k-factor," rather than "ELO." The k-factor is used in the calculations, so posts with that generally are the formulae, or answered with the formulae.