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Calculating Rating Points
The Zone uses the rating formulas established by FIBS (First Internet Backgammon Server). The FIBS rating system uses three factors to calculate the rating adjustments after each match:
- The length of the match.
- Each player's experience.
- The difference in ratings between two players.
Here are the FIBS formulas on how to calculate your Backgammon
rating points. You begin with 1500 rating points. Your rating points will increase when you win a game and decrease when you lose a game. Regardless of your performance, the rating program will never drop your rating below 100 rating points.
Variables:
n = The length of the match P1 = Player 1's current rating P2 = Player 2's current rating E1 = Player 1's experience before the match ends E2 = Player 2's experience before the match ends PE1 = The value calculated for Player 1's experience PE2 = The value calculated for Player 2's experience D = The absolute value of the difference between Player 1's rating and Player 2's rating F = The probability of the favored player winning the match U = The probability of the unfavored player winning the match Experience (E1 and E2) is the running total length of all the completed matches. So if it's your first time playing Backgammon
in a rated room, your experience starts at 0. And after playing a 1-point match game, your experience would be 1. If you play and complete a 3-point match game, then 3 points will be added to your experience value, for a total of 4 points.
Variables that need to be calculated ("sqrt" is "square root," for which there is no symbol in ascii):
D = The absolute value of P1-P2 U = 1/(10 (D * sqrt(n)/2000)
+1) F = 1-U PE1 = Maximum (1, 5 - ((E1 + n)/100)) PE2 = Maximum (1, 5 - ((E2 + n)/100)) To calculate each player's rating:
If Player 1 (P1) has a higher rating than Player 2 (P2) and wins, P1's rating increases by:
4 * PE1 * sqrt(n) * U
If P1 has a higher rating and loses, P1's rating decreases by:
4 * PE1 * sqrt(n) * F
If P1 is rated lower and wins, P1's rating increases by:
4 * PE1 * sqrt(n) * F
If P1 is rated lower and loses, P1's rating decreases by:
4 * PE1 * sqrt(n) * U
To calculate Player 2's rating, substitute PE1 with PE2.
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