Damage calculation is the process of calculating the Battle Damage done to Life Points from an attack and determining which monster(s) is to be destroyed (if any). When an Attack Position monster is destroyed, the damage inflicted is the difference between the ATK of the two monsters. The damage calculates first then the face up monster with lower ATK is destroyed (If two Attack Position monsters with equal ATK battle, both monsters are destroyed).
When a Defense Position monster is destroyed, no damage is inflicted, unless a card effect allows piercing damage. When a direct attack is performed, the damage inflicted is equal to the current ATK of the attacking monster unless stated on the card, as is the case with "Cyberdark Edge".