Common used checking method Weighted modulo 11 Check Formula unit digit x 2 tenth digit x 3 hundredth digit x4 add all mod 11, use 11- the remainderCommon used checking method ◼ Weighted modulo 11 check ◼ Formula : ◼ unit digit X 2 ◼ tenth digit X 3 ◼ hundredth digit X 4 ◼ : ◼ add all, mod 11, use 11 - the remainder