Abilities for general task resolution (1/2)

While thumbing through my Ready Ref Sheets, I noticed this mechanic for resolving extraordinary actions attempted by characters:

"At judge's option, a player may attempt a task, and be successful if he rolls the ability being tested as a percentage or less. For example, a Fighter with a Strength of 15 attempts to roll back a large boulder, rolling a 14% he would be successful."

This is a fun mechanic, because by changing the unit of dice from 3d6 to d100 it puts the difficulty of the task in perspective for the player. But there's an easy way for the referee to tune it according to the difficulty of the task without resorting to +/- percentage modifiers. I'll talk about that tomorrow.