Introdutction:
The check digit is the last digit of an ISBN.
It is calculated on a modulus 11 with weights 10-2,
using X in lieu of 10 where ten would occur as a check digit.
This means that each of the first nine digits of the ISBN
– excluding the check digit itself –
is multiplied by a number ranging from 10 to 2 and
that the resulting sum of the products,
plus the check digit,
must be divisible by 11 without a remainder.
Introdutction:
The check digit is the last digit of an ISBN.
It is calculated on a modulus 11 with weights 10-2,
using X in lieu of 10 where ten would occur as a check digit.
This means that each of the first nine digits of the ISBN
– excluding the check digit itself –
is multiplied by a number ranging from 10 to 2 and
that the resulting sum of the products,
plus the check digit,
must be divisible by 11 without a remainder.
Example:
ISBN 0-8436-1072-7:
Group
identifier |
Publisher
prefix |
Title
identifier |
Check
digit |
|||||||||||
ISBN | 0 | 8 | 4 | 3 | 6 | 1 | 0 | 7 | 2 | 7 | ||||
Weight | 10 | 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | |||||
|
||||||||||||||
Products | 0 | +72 | +32 | +21 | +36 | +5 | +0 | +21 | +4 | +7 |
As 198 can be divided by 11 without remainder 0-8436-1072-7 is a valid ISBN.
7 is the valid check digit.