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 longest word with a dictionary entry, according to Duden is at 36 letters, Kraftfahrzeug-Haftpflichtversicherung, motor vehicle liability insurance. However a 39-letter word, Rechtsschutzversicherungsgesellschaften, insurance companies providing legal protection, is considered the longest German word in everyday use by the Guinness Book of World Records. In theory, a German word can be infinitely long. Unlike in English, an extra concept can simply be added to the existing word indefinitely.