Its a rolling 52 week total point system. Nadal won Wimbledon last year so he can not gain any points this year but Djokovic can since he did not make the final last year, thus he passes him no matter what happens Sunday. His #1 ranking is really on the strength of the Masters series and his domination of those tournaments this year plus being 4-0 versus Nadal, especially when considering if Nadal wins on Sunday he would have won 5 of the last 6 majors.