From publisher blurb: An alternate crit & fumble system and it's a bit more elegant that my other system. This one calls for a percentile roll in addition to the roll to hit, percentage chance of critting or fumbling is dependent on the difference between the to hit number and the to hit die result. Any hit can be a crit and any miss a fumble. In addition, first level puds have a chance of critting without rolling multiple 20's.