The Rankings and Rating should be updated each week, with all the individual Swiss-style events run during the previous week, using the ELO player-rating system. The ELO player-rating system compares players’ match records against their opponents’ match records and determines the probability of the player winning the matchup. This probability factor determines how many points players’ ratings go up or down based on the results of each match. When a player defeats an opponent with a higher rating, the player’s rating goes up more than if he or she defeated a player with a lower rating (since players should defeat opponents who have lower ratings). All new players start out with a base rating of 1600. The following equation is used to determine a player’s win probability in each match: Win Probability = | 1 | | ------------------------------------------------ | 10^((Opponent’s Rating–Player’s Rating)/400) + 1 |
This probability is then used to recalculate each player’s rating after the match. In the equation below, players receive 1 point if they win the match, 0 if they lose, and 0.5 for a draw. Players’ new ratings are determined as follows: | Player’s New Rating = Player’s Old Rating + (K-Value * (Scoring Points–Player’s Win Probability)) |
All players are rated at the beginning with the first match in which they play. Further ratings are calculated chronologically from that first match. | 
