Does your rating count from the start of the game or the end?

I am currently in a game with an opponent who's rating has improved quite a bit during the course of our game; it looks like he may have won three games since we started. When our game concludes will our new ratings be worked out from how they were at the beginning of the game or from what they were at its conclusion?

Thanks.

The conclusion.  I had an experience once where I was playing a player rated at 2454 (more than 750 points above me) when we started our 2-game tournament series.  He suddenly stopped logging in.  He had several hundred games going simultaneously, and after a day or two they started timing out as losses for him, one right after the other, with his rating going down with each loss.  By the time it got to my game in the lineup of timing out games, his rating had plummeted to nearly 300 points below mine.  As a result, my "win" over him only gave me a 5 point gain in rating rather than the large jump I would have gotten had I won back when his rating was 750 points higher than mine. 

Calculating the ratings change after the game concludes leads to a more accurate estimate of strength.

In a strange way it also leads to ratings being less accurate for some. Players who think rating is everything, try to delay losses for as long as possible so they have a higher but less accurate estimate of strength.

Cheers guys, I know the rating system is not perfect and is not the be-all and end-all but it's the only way I have of really rating my progress at the moment so I probably have developed a bit of rating envy! 

 Thanks again.