Ratings system question

How is it worked out? I have just beaten a friend and his rating seemed to go down by 18 points (from 1200ish) and mine up 3 (from 1150ish).

This must have been asked before but I don't have the inclination to trawl through 15000 threads.

No need to trawl through any posts. Try the FAQ under Help, it's explained in there.

Thanks!

I thought I'd looked through all of those but mustn't have been thorough enough.