The ISBN is used as an identifier for books. In teh past this was 10 digits long, but due to growth the number needed to be extended. Most new ISBN of the 13 digit variety start with 978. The problem is that many book sellers do not know how it works and have implimented it incorrectly on their systems. What has happened is in some cases they have taken the 10 digit number and added 978 at the front. for example
10 digit - 0380977087
becomes
13 digit - 9780380977087
This unfortunately is incorrect in the majority of cases, the reason is the last digit of the 10 digit number is a check digit, and is calculated by applying a formula to the previous digits. The purpose of teh check digit is to create a means of identifying a number which has been written in error. The 13 digit code also uses a check digit, but as there are three more numbers at the front, the resulting digit is almost always different to that of teh 10 digit number. In teh case of teh number shown above the result should have been
9780380977086
So as you can see a small error, but enough to make it hard to find a book by ISBN.
In addition to this there are spacers used between different groups of numbers, and there are various formats, so in general it is best to use no spacers.
FAQ answers attributed to Raymond E. Feist are copyright by Raymond E. Feist.
It should also be born in mind that the answer given was only applicable on the date written, and to a specific question. You may find further, similar questions, in the FAQ.
