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.
1 The Arctic lion's mane jellyfish may be the longest animal; the biggest had a bell (body) with a diameter of 2.28 meters (7 feet 6 inches) and the tentacles reached 36.5 meters (120 feet). 2  It was found washed up on the shore of Massachusetts Bay in 1870. 3  Bootlace worms can reach great lengths.