This tutorial help you to understand formula of spells...
setCombatFormula(combat, type, min_a, min_b, max_a, max_b, min_lvl, max_lvl, min_mlvl, max_mlvl, min_dmg, max_dmg)
combat - object of combat :)
type - type of formula (FORMULA_LEVELMAGIC, FORMULA_SKILL, FORMULA_VALUE)...