Let's go. Pikachu's wearing and resisting are two opposite attributes, which literally means the ability of penetrating and resisting magic. They restrain each other. Let's make an analogy for wearing and resisting magic. We will all know.
If a's penetration is 20 and B's resistance is 10, then when a attacks B quickly, B's damage increases by (20-10)%. On the contrary, it will be reduced by 10%. That is to say, the attacker's legal wear minus the defender's legal resistance multiplied by 1% is the actual damage. If the number is positive, the damage will be increased, and if the number is negative, the damage will be reduced.