The new ladder is derived from the previous one in the following steps:
The computation used to work up the March and April ladders was the following.
Unplayed matches are ignored. There are no defaults. If you beat a player rated better
than yourself, it affects both your ratings more than if you beat a worse-rated
player. If Lee Beachill beats you, it doesn't change the world much. But if you
were to beat Lee Beachill, champagne's on the CRFC.
Let HIGHER be the higher-rated player.
Let LOWER be the lower-rated player.
Let DIFF be the difference in ratings, i.e. rating(HIGHER) - rating(LOWER).
Let PERC be the percentage of games won by the winner. (3-0 => 100%; 3-1 => 75% etc.)
Let STEP be the average difference in ratings between two adjacent players in the ladder.
Let ADJ_W be the amount added to the winner's rating.
Let ADJ_L be the amount subtracted from the loser's rating.
If HIGHER beats LOWER:
ADJ_W = PERC * STEP / (1.0 + DIFF/STEP)
ADJ_L = ADJ_W
If LOWER beats HIGHER:
ADJ_W = 2.0 * PERC * (STEP + DIFF)
ADJ_L = 0.5 * PERC * (STEP + DIFF)
The gory details of what Harold does every month is