Physmig 1.14 Chapter: "Calculation of damage dealt in battle". Section "base damage modifier". Quote "in the event that the attacker unit's attack (Att) (taking into account all artifacts) is greater than the victim's defense (Def), for each unit of difference, the modifier increases by 5% of the base damage value (the maximum excess allowed in the game is 300%; if the Attack-Defense delta continues to grow, the effect does not increase)".

Based on what is written, 3 points will give a damage increase of 15%.
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