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.
If Chillal's record-breaking feat is any indication, nails can grow to be pretty long. The longest of Chillal's nails is his thumbnail, which measures 6.5 feet (2 m) long and ends in a tightly wound coil. All of Chillal's fingernails measure different lengths, which is normal since each nail grows at a different rate. Credit: Courtesy of Guinness World Records. View full size image.