The check digit is used to confirm the initial digits of the card number. The benefits of using a checksum is that it prevents casual attempts to invent credit card numbers, as only one in ten will be valid.
Length (adj). the longest, or longer, dimension of any object, in distinction from breadth or width; extent of anything from end to end; the longest line which can be drawn through a body, parallel to its sides; as, the length of a church, or of a ship; the length of a rope or line.
The world's longest goldfish is owned by Joris Gijsbers and measured 47.4 cm (18.7 in) from snout to tail-fin end. It's the size of a house cat! He is a Red Oranda, and he is 15 inches long! The largest recorded goldfish was 17 inches long!