The Power level in this world is divided as :

Bronze

Silver

Gold

Platinum

Diamond

for every tier, it will be divided to 4 levels:

low-level

silver-level

high-level

peak-level

The grade is divided into :

NORMAL

ELITE

PERFECT

EPIC

LEGENDARY

The quality is divided into 2 category the normal one and the system one.

the system one Is range from

F

E

D

C

B

A

AA

S

SS

SSS

EX

the common one that they believe from the stone where it is higher one grade from the system

E = F from the system

D = E from the system

C = D from the system

B = C from the system

A = B from the system

S = A from the system

SS =AA from the system

the MC system quality grading is lower than normal.

just comment the thing that you don't understand.