Originally posted by gregoftheweb
I believe RHP calculates the new ratings based on the player's ratings at the BEGINNING of the match.
In fact, the rating adjustments are calculated based on the players' ratings at the end of the match. There was a thread on this a while back where it was pointed out that this means it is a good idea to finish your losing games before your winning ones.
It would appear that this gives a way to manipulate the system and that it would be preferable to use the starting ratings, but someone gave a convincing argument against this: you could boost your rating unfairly by starting a lot of new games while you had a low rating. In any case, if a player is steadily starting and finishing games, their latest rating is the best measure of how hard it is to beat them.
Don't forget that provisional ratings are calculated in an entirely different way and that the effect of finishing a game against someone with a 'p' rating is half what you would otherwise expect.