# Talk:International Standard Book Number

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## Uniqueness of ISBN's

ISBN's are not unique; I worked in the publishing industry and there are LOTS of ISBN's that are assigned to more than one book. They are assigned to books that don't even share the same title, subject or whatever...

I'd rather start the discussion here than go into the article and change stuff only to have it reverted by a bot. — Preceding unsigned comment added by 108.40.32.125 (talk) 18:36, 9 March 2013 (UTC)

Citation? Examples? Andy Mabbett (Pigsonthewing); Talk to Andy; Andy's edits 20:58, 10 March 2013 (UTC)
ISBN 1-55902-983-8 appears to be used for an entire collection of literary classics - I have "The Time Machine" by H.G. Wells under that ISBN, but if you check out some of the sources autolinked by Wikipedia for that ISBN, you can see that it is far from unique. Yevuard (talk) 01:59, 15 August 2013 (UTC)

Actually ISBN is not unique in a conetxt of a Content Model. Print copy and ebook edition must have different ISBNs... The Wikipedia article not report this problem. Since ISBN is "unique title identifier" (which identifies a particular title or edition of a title) there are many ISBNs for the same content (same copyright). Each language version/adaptation, each edition, and each media type, that can be characterized as different product, may have a different ISBN. The Wikipedia article must explain better this problem. --Krauss (talk) 06:10, 15 September 2014 (UTC)

The indecs Content Model is hardly the Content Model. This is not a problem, it is a feature; if you want an identifier that behaves otherwise, use an identifier designed to behave the way you want. The first sentence under Overview is quite clear: "An ISBN is assigned to each edition and variation (except reprintings) of a book. For example, an ebook, a paperback, and a hardcover edition of the same book would each have a different ISBN." If it were otherwise, you couldn't order ISBN 0-345-44856-7 and know that you're getting a paperback English edition, which would defeat the purpose of ISBNs.--Prosfilaes (talk) 09:16, 15 September 2014 (UTC)
Ok, the first setence change is important (!). About "the model" or "a model" (I changed), you see that it is not the problem: indecs is the real and practical solution used by DOI, we can cite indecs as a good example of content model for "book content", to avoid ambiguities about "what is content". --Krauss (talk) 11:11, 15 September 2014 (UTC)

The standard says ISBN should be unique. Duplicates can be found due to errors made by publishers rather then intentionally grouping different books. --Nux (talk) 18:26, 15 September 2014 (UTC)

Please check my explanation, it is about "content equivalence", not about editorial mistakes... "Print copy and ebook edition must have different ISBNs", yes is a fact... But, another fact is that Print copy and ebook edition have equivalent contents. People today, after 1990's, Web advent, tablet computers, etc., people today see ebook and book as the same target-product, that is the content. --Krauss (talk) 21:26, 15 September 2014 (UTC)

### Need for more explanation or a section about

ISBN uniqueness is "media/edition"-oriented identification of books, as explained above, and made sense in the 1970s. In the 1990s and onward, with PCs, good screens, and the Web, what makes sense is to consider only content, independent of media. A ISBN can not used in a typical database of books as public ID because is not unique (all databases must generate an internal unique ID for this task). For the same reason, the use of ISBN as URN was was not widespread.

This "content-oriented identification" of books' is a repressed demand today (2010's)... So, this kind of non-uniqueness (in a content perspective) is a real and relevant problem.

--Krauss (talk) 11:11, 15 September 2014 (UTC)

PS: a solution is possible, a TC 46/SC 9's rule that elects one (ex. the first) ISBN to group the others, representing all the "same-content ISBNs"... And a online service that resolves this "unique ISBN", as xISBN do today.

Actually in terms of copyright each translation is copyrighted by the translator (and possibly publisher) and having a book doesn't give you the right to use e-book and vice versa. So ISBN should be unique for each edition (e-book, CD, paper -- all different editions). I said it SHOULD, because there are some cases where it is not (as discussed above). --Nux (talk) 18:26, 15 September 2014 (UTC)
Ops, sorry, here in this subsection we not dissuing translations, only "media/edition" (see above). Usually media/edition changes not change the content... As suggested before, see DOI identified articles (ex. into different medias) to undertand the problem/models/etc. You can also see the Linking ISSN as reference-model to a "unique ISBN". --Krauss (talk) 21:03, 15 September 2014 (UTC)
About my commented (PS) "solution": see ISSN-L and imagine an ISBN-L. Only imagine, I not discussing here de uniqueness of ISBN (that is necessary for comertial needs, each media is a distinct product), but the necessity and the nowadays-lack of a ISBN-L. --Krauss (talk) 21:13, 15 September 2014 (UTC)
It seems to me you are trying to create reality rather then describe it and this is not what Wikipedia is about. We are not researching for solutions. We are describing solutions proven by authorities in appropriate places. See WP:OR. --Nux (talk) 23:19, 15 September 2014 (UTC)

## ISBN-10 check digit calculation

Hi, While I think it's good to have the single formula for calculating the check digit, which uses modular arithmetic, I think this is too complicated and inaccessible for 99% of readers, who won't know what 'mod' and modular arithmetic is, and won't be inclined to find out, just so they can understand this long formula. Which is unfortunate, as finding the check digit is actually quite simple, and doesn't need to use the language of modular arithmetic. Therefore I think an initial explanation along the lines of the following would enable a lot more people to understand this. Other editors' thoughts? Thanks Mmitchell10 (talk) 06:49, 25 September 2014 (UTC)

The value of the check digit is simply the number which needs to be added to the total of the first nine digits, each multiplied by its weight (descending from 10 to 2), so that the total is the next multiple of 11.

For example, for an ISBN-10 of 0-306-40615-?, the total of the first nine digits is:

{\displaystyle {\begin{aligned}s&=(0\times 10)+(3\times 9)+(0\times 8)+(6\times 7)+(4\times 6)+(0\times 5)+(6\times 4)+(1\times 3)+(5\times 2)\\&=130=(11\times 11)+9\end{aligned}}}

The next multiple of 11 is 132, therefore the check digit is 2.

I agree that the Modular arithmetic article lacks a section with a clear and basic explanation of what it is and how to perform such calculations using ×, ÷, + and -. However, that is an issue for that page. In fact it is a very strong reason to include such an explanation in that article. It is not a reason to include such an explanation in this article unless it is impossible to have a basic explanation of modular arithmetic in the linked article. — Makyen (talk) 17:54, 2 October 2014 (UTC)
I think I would say that, rather than being an explanation of how to do modular arithmetic, it's an explanation of how to find the check digit without needing to use modular arithmetic. After all, modular arithmetic isn't a necessary part of ISBN calculations or proofs (if memory serves), it's just an alternative/smarter way of handling them. Mmitchell10 (talk) 21:14, 13 October 2014 (UTC)

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## Bug in ISBN-13 check digit calculation example

The "ISBN-13 check digit calculation" section includes an example with:

For example, the ISBN-13 check digit of 978-0-306-40615-? is calculated as follows:

s = 9×1 + 7×3 + 8×1 + 0×3 + 3×1 + 0×3 + 6×1 + 4×3 + 0×1 + 6×3 + 1×1 + 5×3
=   9 +  21 +   8 +   0 +   3 +   0 +   6 +  12 +   0 +  18 +   1 +  15
= 93
93 / 10 = 9 remainder 3
10 –  3 = 7


That's fine for 978-0-306-40615-? but if the number had been 978-0-306-40614-? we would have:

s = 9×1 + 7×3 + 8×1 + 0×3 + 3×1 + 0×3 + 6×1 + 4×3 + 0×1 + 6×3 + 1×1 + 4×3
=   9 +  21 +   8 +   0 +   3 +   0 +   6 +  12 +   0 +  18 +   1 +  12
= 90
90 / 10 = 9 remainder 0
10 –  0 = 10


I highlighted the part that changes so that you can see what's different.

The issue is that computed check digit is "10". We need to do another mod 10 on it but I'm not sure of the best way to show this. For example: we could do it all in one line:

  ...
= 90
(10 - (90 mod 10)) mod 10 = 0


Or would it be easier to understand if it broken down to more than one line?

  ...
= 90
(10 - (90 mod 10)) = 10
10 mod 10 = 0


An issue with the proposed fixed is that in the #ISBN-10 check digit calculation talk section which is above this there's talk about avoiding modular arithmetic in the examples. --Marc Kupper|talk 06:51, 20 March 2016 (UTC)