^ abcdeInternational ISBN Agency (2012). ISBN Users' manual(PDF). isbn-international.org (Sixth International ed.). pp. 7, 23. ISBNArchived(PDF) from the original on 29 April 2014. Retrieved 29 April 2014.
^Some books have several codes in the first block: e.g. A. M. Yaglom's Correlation Theory..., published by Springer Verlag, has two ISBNs, 0-387-96331-6 and 3-540-96331-6. Though Springer's 387 and 540 codes are different for English (0) and German (3); the same item number 96331 produces the same check digit: 6. Springer uses 431 as their publisher code for Japanese (4) and 4-431-96331-? would also have check digit ? = 6. Other Springer books in English have publisher code 817, and 0-817-96331-? would also get check digit ? = 6. This suggests special considerations were made for assigning Springer's publisher codes, as random assignments of different publisher codes would not lead the same item number to get the same check digit every time. Finding publisher codes for English and German, say, with this effect amounts to solving a linear equation in modular arithmetic.
^The International ISBN agency's ISBN User's Manual says: "The ten-digit number is divided into four parts of variable length, which must be separated clearly, by hyphens or spaces" although omission of separators is permitted for internal data processing. If present, hyphens must be correctly placed; see ISBN hyphenation definition. The actual definition for hyphenation contains more than 220 different registration group elements with each one broken down into a few to several ranges for the length of the registrant element (more than 1,000 total). The document defining the ranges, listed by agency, is 29 pages.
^Canada, Library and Archives. "ISBN Canada". www.bac-lac.gc.ca. Retrieved 2016-01-19.
^"ISBN Ranges". isbn-international.org. 29 April 2014. Select the format you desire and click on the Generate button. Archived from the original on 29 April 2014. Retrieved 29 April 2014.
^See a complete list of group identifiers. ISBN.org sometimes calls them group numbers. Their table of identifiers now refers to ISBN prefix ranges, which must be assumed to be group identifier ranges.
^Hailman, Jack Parker (2008). Coding and redundancy: man-made and animal-evolved signals. Harvard University Press. p. 209. ISBN978-0-674-02795-4.