The Magic Formula aptitude (術式適性 Jutsushiki tekisei, localized as Ars Magus aptitude) is an ability score for using Magic Formulas. The higher the score, the greater one’s ability.
The Magic Formula aptitude tests (術式適性検査 Jutsushiki tekisei kensa)[1] are carried out in the Military Academy while assessing new students. It is a simple test that is based on Magic Formula synchronicity that consist of activating a base Magic Formula. The aptitude is measured by the amount of magic element that the tester requires to activate it. An average human requires using more of the element for the activation, while someone like Taokaka needs less of it. Noel Vermillion was accepted to the Academy after receiving the highest Magic Formula aptitude score in history.
Before obtaining the Blue Grimoire, Ragna’s Magic Formula aptitude was very low, and he was unable to use Magic Formulas at all.