From the Introduction:
The alignment system in d20 games is difficult to use because there are no definite game rules covering alignment. Vital to any alignment system are rules to govern alignment shifts. Normally, it is left to the DM to decide if a player portrays his character's alignment correctly. If the player's roleplaying is found lacking, then the DM must use his own judgment, and the few guidelines given in the rulebooks, to decide if an alignment shift is appropriate. There are no game mechanics to fall back on.
In this system, both the ethical (law-chaos) and moral (good-evil) components of alignment are given a score on a scale of 0 to 20. The number 10 represents neutrality on both axes. Scores of 20 indicate a maximum of law and good, while scores of 0 indicate a maximum of chaos and evil. Thus, a thoroughly chaotic good character would have an ethics score of 0 and a morality score of 20. Conversely, a diabolically lawful evil character would have a 20 in ethics and a 0 in morality.