Elo

Elo is a rating system used to determine the relative skill of individuals. It is commonly used in games such as Chess.

In Elo, each player is given a rating; it may be an existing rating or seeded from an existing rating; for example, Chess games may seed players with a ranking around 1500 for average players (or lower if the player believes to be inexperienced.)

Rating
Scored in Elo change based on matches or other events. The following values are used:


 * RA, rating for player A.
 * RB, rating for player B.
 * $$E_A = \frac{1}{1+10^{(R_B - R_A)/400}} $$, the expected score of player A.
 * $$E_B = \frac{1}{1+10^{(R_A - R_B)/400}} $$, the expected score of player B.
 * K, an adjustment factor (high for new players, or lower for more experienced ones)
 * $$S_A$$ and $$S_B$$, the scores for players A and B
 * $$R'_A = R_A + K_A(S_A - E_A)$$, the new rating for player A
 * $$R'_B = R_B + K_B(S_B - E_B)$$, the new rating for player B