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 decimeter (dm) is the next largest unit of length and equals 1/10 of a meter. 2  The meter (m) is the next largest unit of length. 3  The dekameter (dam) is the next largest unit of length and equals 10 meters.  The hectometer (hm) is the next largest unit of length and equals 100 meters.