Dragon uses the EGF rating system for its calculus. You can find details on the EGF rating system algorithm at

EGF Go Rating Pages.

Given the board size, handicap and komi, the implied initial rating difference (the difference that would have given this <home faq.php?read=t&cat=357#Entry98 >Proper Handicap) can be calculated. This is compared with the final rating difference (at the end of the game) to decide the real advantage a player had. The probability of the result is calculated using the EGF algorithms in which the constants used are the existing values from EGF statistics. Knowing this probability, it is determined whether a player has done better or worse than expected, whether the rating should be increased or decreased. The magnitude of the change is calculated from this probability and weighted by a factor depending upon the board size, and the ratio of the confidence intervals (the

Blue Area in the rating graph) of the two players.

For example, in an

*even* game where the rating of Black is less than White's, the probable result is that White will win.

- If White wins, White's rating may increase slightly or possibly not at all, since this White's win was expected. Based on the same reasoning, Black's rating may a little or may remain the same.

- If Black wins, Black's rating will be increased by a greater amount, since this was not expected. On the same basis, White will suffer a bigger drop in rating.

The size of win is not taken into account. A player may win by half a point or by 100 points. In the same circumstances those wins would be equal in terms of rating change difference computed by DGS.