Current ranges of people, artifacts, spells etc from the world of the novel.
Common (first-second-third level) _____
G (- |+)
F (- |+)
E (- |+)
____Special (first-second level)
D (- |+)
C (- |+)
_________Earth (first-second-third level)____
B(- |+)
To (- |+)
S (- |+)
_______Heaven (First level)_______
SS (- |+)
The quality of an artifact is classified into common, special, earth and sky, each name contains a range.
For example 2nd level Earth quality spells, it means that it is an A rank spell so to speak.
The grade of the spell, weapon, etc, means the level that is taken into account in that range, for example a 2nd level Earth quality spell is an A rank spell, the grade tells me the level that is in that range, what it means that if I take the previous example and add a low grade, it means that it is an A-, if I say that it is medium then it is an A, and if I say that it is high then it is an A+.
The same goes for artifacts and such.
PS: "|" means medium too