Short answer: A class 1 would be someone like Ptolemy. Someone so strong they had a W.M.D. named after them.

Long answer: The classification system is based off of personal experience (i.e., experience from every owner of the sword) based off of the rings reaction to a large number of magic users. It works by detecting the magic they give off. The stronger the magic, the higher the class. However, the better a magic user is, the less their inexperience will interfere with their magic, so the more potent the magic they give off will be. A level 2, like strange, is someone who has a mastery of magic. Not a specific magic, mind, like our Russian friend, but magic in general.
To get to the upper classifications takes something not-human. Basically, you have to start making the jump from a person to a monster to become that powerful. There is one level above class 1, which is class O. Not Zero, mind, but O. As in 'Oh!,' the sudden declaration of clairvoyant understanding that precedes the phrase, "we're fucked." At that point, you've gone from 'was human, is now monster' to just... 'is a monster.'