The rating formula is based on the opponent's rating and the score difference. You can win or lose somewhere between 0 and 40 points. Suppose your rating is r1 , and the opponent's is r2. Let w be 1 if you win , .5 if you draw, and 0 if you lose.
After a game, your new rating will be:
r1 + k * [w - ----------------------]
1 + 10 ^ ((r2-r1)/400)
where, k = 20 + ---
|d| - score difference - can have values between 0 - 200
If you're playing a provisional player , k is scaled by (11 - n), where n is one plus the number of games your opponent has played.
The formula used for provisional players is based on the average rating of his opponents and the number of wins and losses. This formula can have a strange behavior since you can lose points after winning a game if your opponent rating is below average:
m + 133 * ln(w/l)
m - opponents rating average
w - number of wins
l - number of losses
If both players are provisional there will be no rating change.
You can see how your rating will be affected before the game starts. Click on the person's name and select [assess] , also you can type 'assess name' in the command mode.
SEE ALSO : provisional , assess