The PIF ATP rankings[1] are the Association of Tennis Professionals' (ATP) merit-based system for determining the rankings in men's tennis. The top-ranked player is the player who, over the previous 52 weeks, has garnered the most ranking points on the ATP Tour. Points are awarded based on how far a player advances in tournaments and the category of those tournaments. The ATP has used a computerized system for determining the rankings since August 23, 1973.[2] Starting in 1979, an updated rankings list is released at the beginning of each week. Since 1973, 29 players have been ranked No. 1 by the ATP,[3][4] of which 19 have been year-end No. 1.