Power/Speed Number is one of many Baseball statistics created by Sabermetric god Bill James. PSN, as it's sometimes abbreviated, is designed to evaluate a player's ability to both hit for power and steal bases. It can be found by using the following formula:
PSN = (HR*SB*2)/(HR+SB)
The top Power/Speed man of all time is Barry Bonds at 546.49 prior to the start of the 2003 season. Rickey Henderson comes in next, at 487.5 and Willie Mays trails at 447.1. Alex Rodriguez holds the single-season mark for his 1998 season in which he hit 42 home runs and stole 46 bases, giving him a mark of 43.91. Other active players who regularly put up high Power/Speed Numbers are Vladimir Guerrero, Preston Wilson, and Alfonso Soriano.
While Power/Speed Number can't tell you everything about a player, it's worth noting that of the top 10, four are in the Hall of Fame (Willie Mays - 3, Joe Morgan - 5, Hank Aaron - 7, Reggie Jackson - 8), three are sure-fire candidates when they retire (Barry Bonds, Rickey Henderson, Sammy Sosa), and Andre Dawson - 6 is currently a promising candidate on the ballot.