I googled and found the following: http://www.isbn.org/standards/home/isbn/us/isbnqa.asp#Q5 Why do some ISBNs end in an "X"? In the case of the check digit, the last digit of the ISBN, the upper case X can appear. The method of determining the check digit for the ISBN is the modulus 11 with the weighting factors 10 to 1. The Roman numeral X is used in lieu of 10 where ten would occur as a check digit." WWhat you may ask, is a check digit. (At least I wanted to know.) I found a simple definition after a while: The source below not only explains what a check digit is, but discusses several different kinds besides ISBN check digits. http://www.augustana.ab.ca/~mohrj/algorithms/checkdigit.html "Check Digit A decimal (or alphanumeric) digit added to a number for the purpose of detecting the sorts of errors humans typically make on data entry. When human beings use numbers - whether keying them into computers, dialing them on telephones, or reading them and telling them to others --- they tend to make certain kinds of mistakes more often than others. According to Richard Hamming (Coding and Information Theory, 2e, Prentice-Hall, 1986, p. 27), the two most common human errors are: * Interchanging adjacent digits of numbers: 67 becomes 76 * Doubling the wrong one of a triple of digits, two adjacent ones of which are the same: 667 becomes 677" A couple of sources explain how the ISBN check digit is arrived at. Jake and probably other mathematicians would possibly understand it--it seems to have to do with adding the digits in the ISBN number and dividing by 11. Here's a URL if you want to read more about it. (I'm more into words than numbers--I gave up quickly on trying to solve even the easiest Siduko so I wona't give the explanation here. You can look it up yourself.) smile) http://www.cs.queensu.ca/~bradbury/checkdigit/isbncheck.htm or a fuller explanation of why and what the parts of an ISBN number stand for, read this: http://www.isbn.org/standards/home/isbn/us/isbnqa.asp What is an ISBN? The International Standard Book Number (ISBN) is a 10-digit number that uniquely identifies books and book-like products published internationally. What is the purpose of an ISBN? The purpose of the ISBN is to establish and identify one title or edition of a title from one specific publisher and is unique to that edition, allowing for more efficient marketing of products by booksellers, libraries, universities, wholesalers and distributors. What is the format of the ISBN? Every ISBN consists of ten digits and whenever it is printed it is preceded by the letters ISBN. The ten-digit number is divided into four parts of variable length, each part separated by a hyphen. Does the ISBN have any meaning imbedded in the numbers? The four parts of an ISBN are as follows: Group or country identifier which identifies a national or geographic grouping of publishers; Publisher identifier which identifies a particular publisher within a group; Title identifier which identifies a particular title or edition of a title; Check digit is the single digit at the end of the ISBN which validates the ISBN." "Does the ISBN have any meaning imbedded in the numbers? The four parts of an ISBN are as follows: Group or country identifier which identifies a national or geographic grouping of publishers; Publisher identifier which identifies a particular publisher within a group; Title identifier which identifies a particular title or edition of a title; Check digit is the single digit at the end of the ISBN which validates the ISBN." --- Evan Reese <mentat1@xxxxxxxxxxxxxx> wrote: > I have a book with an ISBN with an X at the end of > it, such as: > ISBN: 0-7564-0326-X > > I have encountered this before, but not often, and > was wondering if anyone here knows what the X > signifies. > > > Thanks. > __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com To unsubscribe from this list send a blank Email to bksvol-discuss-request@xxxxxxxxxxxxx put the word 'unsubscribe' by itself in the subject line. To get a list of available commands, put the word 'help' by itself in the subject line.