http://en.wikipedia.org/wiki/Elo_rating_system#Theory
"The maximum possible adjustment per game, called the K-factor, was set at K = 16 for masters and K = 32 for weaker players."
As for "why" the formula is the way it is, it's because (I think) he was trying to make it fit a normal distribution... AKA the bell curve, which you might have heard of.
If you read both wiki pages and still have questions take an intro to statistics class :p
I've been trying to figure out how ELO works. I understand it is a rating system, but I don't understand how it works.
When you are rated 200 points above someone you supposedly have a 75% chance of winning. The formula is 1 / 1 + 10^((RB-RA)/400). I get that. I just don't understand why.
One thing I really don't get is K-value. Who determines that and how does it affect the formula above.
There is limited amount of information about this on the internet. Everything is League of Legends crap that I don't care about. Wikipedia did not answer my questions either.