CitelleRead the number from the publication
Copy the ISBN from the copyright page or its labelled barcode area. Keep an edition note beside it, such as paperback, hardback or electronic format. Different product forms can have different ISBNs even when the title is the same.
Remove presentation spaces and hyphens for the arithmetic, but do not replace unclear characters by guesswork. An ISBN-10 may end with X; that symbol represents a check value of ten in its final position.
Understand the two checks
For ISBN-13, the first twelve digits receive alternating weights of one and three. The final digit makes the weighted total divisible by ten. Current ISBN-13 numbers begin with the ISBN prefixes 978 or 979.
For ISBN-10, the ten positions receive descending weights from ten to one, and the weighted total must be divisible by eleven. For a simple practice pair, 0-306-40615-2 and 978-0-306-40615-7 pass their respective checks. Their validity is not a title lookup.
Then match the edition
After a checksum passes, compare title, authors, publisher, edition and year with a reliable catalogue or the publication itself. A correctly typed number for a different format is still the wrong source for an edition-specific quotation.
Citelle's iPhone app can scan an ISBN barcode and retrieve source records. Keep reviewing those fields: a successful lookup saves typing, while a final reference still needs to describe the version you actually used.
- Treat a failed check as a prompt to reread the number.
- Do not invent a missing digit just to obtain a pass.
- Keep identifier validation separate from content verification.