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From: dhelm@ibmpcug.co.uk (D Helm)
Newsgroups: comp.misc,connect.audit
Subject: ISBN Check Digit Validation
Keywords: ISBN, Validation, Check Digit
Message-ID: <1991May22.170231.5757@ibmpcug.co.uk>
Date: 22 May 91 17:02:31 GMT
Organization: The IBM PC User Group, UK.
Lines: 52

>>In <1991May19.022623.2905@solbourne.com> imp@solbourne.com (Warner Losh) writes:
>>Does anybody know the checksum procedure for ISBN book numbers?

>1 * 1st digit + 2 * 2nd digit + 3 * 3rd digit + ... + 10 * 10th digit
>must be divisible by 11.

>Sometimes the last digit is an 'X'; that's a Roman digit with value 10.
>Hans Mulder    hansm@cs.kun.nl

Almost - to calculate an ISBN checkdigit:

From Left to Right take each digit and multiply by Weight factor.

Test ISBN = 090169049


ISBN             ISBN           Weight                      Total
Digit            Digit          Factor
Position

1st                0            10                              0
2nd                9             9                             81
3rd                0             8                              0
4th                1             7                              7
5th                6             6                             36
6th                9             5                             45
7th                0             4                              0
8th                4             3                             12
9th                9             2                             18
                                                            --------
                                                Total         199
                                                            --------

Divide Total by 11 = 18 remainder 1

Subtract Remainder from 11 = 10

If the result = 0 - 9 then this is the check digit = result
If the result = 10 then check digit = X.


Hope this helps.

Dave H.

Disclaimer: I work for the company - they don't own me.

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