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Regarding the rating: the system has been changed periodically, but in the latest updates of the HD mod, obscure elements have been almost completely removed.
The rating in the lobby now is simply an ELO rating with a coefficient that depends on the map size.
The current rule for changing the rating as a result of a game is as follows:
R1 += K*(RES - 1/(1 + 10^((R2 - R1)/400)))
R2 -= K*(RES - 1/(1 + 10^((R2 - R1)/400)))
Here, R1 is the rating of the first player, R2 is the rating of the second player. RES is 1 if the first player wins; 0.5 if it's a draw; 0 if the second player wins.
The coefficient K depends on the size of the map being played:
K = 60 * ([map width in cells] * (1.5, if with a Dungeon) / (144 * 1.5)).
For example:
XL+U: K = 60
L+U: K = 45
XL-U: K = 40
L-U: K = 30
M-U: K = 20