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.
It is not well known, but giant oarfish are thought to frequent depths around 3,300 feet (1,000 meters). Giant oarfish are the longest known living species of bony fish, reaching a length of 56 feet (17 meters). They can weigh up to 600 pounds (270 kilograms).