Alternative rating.

In the Elo rating system, it is accepted that the transition from one class of play to the next occurs approximately every 200 rating points. If the difference between two players is 200 points, the stronger player wins with a probability of 76%; if the difference is 400 points, the probability will be 91%. A difference of 600 points means the stronger player wins almost always (97%). If the ratings of both players are equal, the probability of either one winning is 50%. These probabilities, of course, do not take into account a player's current form on a given day. At the lowest class level, the Elo rating more often gives incorrect predictions of results, as players of this class make unpredictable mistakes more frequently.

The less often a chess player loses, the more accurately their rating can be assessed. The most accurate rating can be obtained from tournaments where players of roughly equal strength compete. The Elo rating system is based on the assumption that the strength of each chess player can be represented as a probabilistic variable following a normal distribution. The calculation of a specific player's rating based on the results of a tournament is founded on comparing the number of points they scored with the expected number of points predicted based on their rating. If, at the end of the tournament, the number of points scored turns out to be greater than the predicted value, that player's rating increases. If, at the end of the tournament, the number of points scored turns out to be less than the predicted value, that player's rating decreases.