The truth is we could use any multiplier for per minute stats: 10, 12, 40, 48, pi, the square root of 2, or the national debt. The number 40 was taken because in today?s NBA the best players average about that many minutes. What?s important to remember is that per 40 minute stats is not advocating that the coach should give that player 40 minutes a night. When someone mentions that Mariano Rivera had a 1.38 ERA, they?re not saying that Mo should go out and throw all 9 innings. Nor are they saying that if Rivera pitched 9 innings, the opposition would score less than a run and a half per game.