You use your understanding of math to increase your magical output.
Prerequisite(s): Intelligence 5+
Benefit(s): Find the digital root of your mental ability scores. (Example: Int of 5, Wis of 2, Cha of 3 results in the following math... 5 + 2 + 3 = 10, 1 + 0 = 1. Thus the digital root of 5, 2, 3 is 1.) The result gained is then added as a circumstance bonus onto the attack of spells cast.
In addition to doing this, you can choose to cause "Digital Overflow" through your spells cast. Take the digital root gained and test it against a Spellcraft check (DC = 10 + Double Casting Stat + Digital Root). On a successful check, you overcharge the spell with magical potential and reduce the MP cost of the spell by 2. Doing this forgoes the bonus on attack. On a failure, the spell is instead cast at a higher intensity but with maximal output - the bonus on attack is doubled and then applied, but the spell doubles its MP cost rather than increasing.
Using Digital Root uses up 1 additional points from the caster's Magic Pool (unless the caster does a successful Digital Overflow). This isn't added to the MP result if you are forced to double the MP cost of the spell.