Information: Power Ranking - Class and Level
In Academy city powers are ranked through their Level, which is a means of seeing how far they have progressed through the Power Curriculum Program, with Level 0 being the lowest and the Theoretical Level 6 being the highest.
However, there is another means of Ranking abilities that is far less used, which is the Class System. The Class System ranks abilities based the generated effect that the power is capable of achieving. The Highest Rank on the Class System is Rank √-1, has only one a pair of words scrawled under it in the notes 'Image Breaker'.
Below that are Ranks I-X. The creator of this system posits that were two people of the same Level to fight, the one whose power is of a higher Class would win. The thought experiment used as an example for this is:
Class III, Level 5 - Electromaster would lose to a Class IV, Level 5 - Radio Noise, who would also lose to a Class VI, Level 5 - Railgun.
One of the major reasons that this system is derided and oft ignored is the theory of
Class Shift, or the capacity for someone who has a power to work and develop the power in such a way that it evolves to a more advanced variation of the same ability. It is theorized that Misaka Mikoto first came to the city as a Class III, Level 1 - Electromaster, but has undergone a Class Shift Three times, with two of them expected to have happened during a Level Shift when Misaka's abilities evolved enough during a short enough time period to advance multiple levels during a single Level Shift.