You mean the levels? For batting each level is divided into 256 points. So level 0 = 0 to 255, level 1 = 256 to 512 and so on. Anarchy suggested on page 5 in his guide that the level for a world class player is 7. The rest of them (from 8 to 255) are included because it's possible to have them in the game, up to a max of 65535 (= level 255). So it's basically for cheating. The minimum for batting ability is 160 though, so if you select level 0 it generates a number between 160 and 255, not 0 and 255. Also if you enter a number less than 0 it defaults it to 160.
As for bowling the minimum is 320 and maximum is 3168 based on my tests. These are also split into levels where level 0 is world class (Anarchy's guide) and level 12 is the worst possible bowler. His guide goes up to level 6 or 7 (not too sure at the moment), but the game allows for up to 3168 (i.e. level 12) so I included it.