PlayerClassLevelInfo target_classInfo;
PlayerClassLevelInfo owner_classInfo;

float targetBaseHealth = 0.0f;
float ownerBaseHealth = 0.0f;
int incBaseHealth = 0;

for (uint32 i = MIN_CLASSES; i < MAX_CLASSES; i++)
{
    if (i == 6 || i == 10)
        continue;

    sObjectMgr.GetPlayerClassLevelInfo(i, target_level, &target_classInfo);
    sObjectMgr.GetPlayerClassLevelInfo(i, owner_level, &owner_classInfo);

    targetBaseHealth += target_classInfo.basehealth;
    ownerBaseHealth += owner_classInfo.basehealth;

    incBaseHealth++;
}

targetBaseHealth /= incBaseHealth;
ownerBaseHealth /= incBaseHealth;

float damage_percent = olddamage / ownerBaseHealth;
float damage_scaled = damage_percent * targetBaseHealth;

damage = damage_scaled;