It is an absolute rating system, i.e. the rating can be used to determine the winning odds of a specific
player against another specific player. The system has been worked out according to statistical and probability theory.
The rating is an integer, the minimum is 0. The starting rate of an unknown player is 0.
Rating difference | Probability of win |
---|---|
0 | 0.50 |
100 | 0.64 |
200 | 0.76 |
400 | 0.91 |
800 | 0.99 |
Ratings are amended each time you finish a game, by adding or subtracting a small amount from your previous rating value. The amount added or subtracted depends on the result of the game and the rating of the players.
CalculationThis formula has the property that the sum of the rating changes is zero. It turns out that if the rating difference is more then 719 points, then if the strong player wins, there is no change in either rating.
Daily decreaseOverall ratings are decreased each day by an amount depending on the current rating.
The following formula is used:
Rn = ( Ro * Ro ) / 125000
Rn is the new rating.
Ro the old (previous day) rating.
Rating | Amount subtracted |
---|---|
below 353 | 1 |
354-500 | 2 |
501-612 | 3 |
613-707 | 4 |
708-790 | 5 |
791-866 | 6 |
867-935 | 7 |
936-1000 | 8 |
Playing a series of games against the same opponent within a given
time interval will adjust the calculation as follows:
The expected score is calculated for the series of games from the pre-match rating-difference of the two players,
and the ratings are amended based on the expected score and the actual score of the series of games.
These are basically the extensions of the above calculation for more games played.
However, as more matches will reflect the skill difference more precisely, the amendment is raised based on the number of games played.
Number of games in a series of games |
Maximum rating change |
---|---|
1 | 16 |
2 | 24 |
3 | 28 |
4 | 30 |
5 | 31 |
infinite | 32 |
Grand Master | Above 480 | |
Master | 350 - 479 | |
Expert | 240 - 349 | |
Advanced | 150 - 239 | |
Intermediate | 80 - 149 | |
Amateur | 30 - 79 | |
Novice | 0 - 29 |