[ Severus nods. Erik gets the basic principles of it, which is helpful for further conversation; Severus is not actually a very good teacher owing to his impatience with explaining anything. ]

There must be rules, [ is an agreement, ] or set parameters. That's what these are for-- [ Severus slides his diagrams to the center of the table. ] Spellwork is largely instinctive but it can be broken down and mapped out like this. It's sometimes easier to make adjustments when there are equations down to the most finite of variables.

[ He taps a certain design, intersected by lines and numbers look idfk how to explain wizard math i can't even add, then moves to another paper and points to the same design - in a different place, in the middle of a much different diagram. ]

Patterns emerge.