The Harkness system was reasonably fair, but in some circumstances gave rise to ratings which many observers considered inaccurate. The USCF used a numerical ratings system, devised by Kenneth Harkness, to allow members to track their individual progress in terms other than tournament wins and losses. 4.1 Game activity versus protecting one's ratingĪrpad Elo was a master-level chess player and an active participant in the United States Chess Federation (USCF) from its founding in 1939.2.3 United States Chess Federation ratings.

Players whose ratings are too low or too high should, in the long run, do better or worse correspondingly than the rating system predicts and thus gain or lose rating points until the ratings reflect their true playing strength.Įlo ratings are comparative only, and are valid only within the rating pool in which they were calculated, rather than being an absolute measure of a player's strength. This means that this rating system is self-correcting. The lower-rated player will also gain a few points from the higher rated player in the event of a draw. However, if the lower-rated player scores an upset win, many rating points will be transferred. If the higher-rated player wins, then only a few rating points will be taken from the lower-rated player. The difference between the ratings of the winner and loser determines the total number of points gained or lost after a game. After every game, the winning player takes points from the losing one. A player whose rating is 100 points greater than their opponent's is expected to score 64% if the difference is 200 points, then the expected score for the stronger player is 76%.Ī player's Elo rating is represented by a number which may change depending on the outcome of rated games played. Two players with equal ratings who play against each other are expected to score an equal number of wins. The difference in the ratings between two players serves as a predictor of the outcome of a match. The Elo system was originally invented as an improved chess-rating system over the previously used Harkness system, but is also used as a rating system in association football, American football, baseball, basketball, pool, table tennis, and various board games and esports. It is named after its creator Arpad Elo, a Hungarian-American physics professor. The Elo rating system is a method for calculating the relative skill levels of players in zero-sum games such as chess. Arpad Elo, the inventor of the Elo rating system

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