Day 270~377

An ISBN is an International Standard Book Number. ISBNs were 10 digits in length up to the end of December 2006, but since 1 January 2007 they now always consist of 13 digits. ISBNs are calculated using a specific mathematical formula and include a check digit to validate the number. Each ISBN consists of 5 elements with each section being separated by spaces or hyphens. Three of the five elements may be of varying length: • Prefix element – currently this can only be either 978 or 979. It is always 3 digits in length • Registration group element –…