rating calculation quesion.

In have seen the formula for rating-calculation, in the FAQ, in which the new rating is calculated with both players previous rating as parameters. The question the help-side didn't answer for me is: Is it based on the rating me and my opponent has when our game start or when our game ends? I think it should be based on the score we have when tha game starts.

It is based on ratings at the end of the game, as it should be. See my first game, long-since completed, with lionel. He trounced me miserably. Bothe our ratings were around 1200 at the start, but by the end his was in the 1600 range, and mine around 1300. Thus the rating at the end reflected the actual quality of play as exhibited in the game.

Ok, I see the advantage for newly joined players. But when the ranking has settled, wouldnt it be better if you knew from start of games what changes a win or loss will result in?

When the ranking has settled, it is not likely to change a great deal on either side, and as such, whether it is calculated at beginning or end is of little consequence. You will note that there is a practice called "lagarating", in which there is an impending loss to a lower-rated player who obviously is very skilled and will be highly-rated very soon. One lagarates by waiting for his opponent's rating to increase dramatically, and cut his losses.

The system isn't perfect, but it's quite efficient and actually quite mathematically elegant.