Formula of penalty for using a weapon below required level

[Womos]

I noticed that on all TFSs including TFS 1.3 there is this basic formula which just reduce your damage by half if you're below required level
weapons.cpp:

int32_t damageModifier = 100;
        if (player->getLevel() < getReqLevel()) {
            damageModifier = (isWieldedUnproperly() ? damageModifier / 2 : 0);
        }

        if (player->getMagicLevel() < getReqMagLv()) {
            damageModifier = (isWieldedUnproperly() ? damageModifier / 2 : 0);
        }
        return damageModifier;
    }

    return 100;
}

When on real tibia it works that the weapon will loose 1 attack for every level your missing.
Anyone know how to do this?