Spell Mastery
20% Able to understand how the spell works and how to use it.
40% Able to use the spell but weak in terms of power.
60% Able to understand and use the spell consistently.
80% Able to use the spell expertly and apply your own understanding of the spell.
100% Able to use the spell completely and execute the spell masterfully while experimenting with different applications it can be used for.
Spell Mastery would be how much u have mastered said spell and how you use it from now I'll be using different words to assess the mastery over a spell or charm.
Beginner = 20%
Intermediate = 40%
Advanced = 60%
Expert = 80%
Master = 100%
Pretty self-explanatory there.