GTIN codes end in a check digit computed by alternating weights of 3 and 1 across the preceding digits. ISBN-10 uses a different scheme entirely, mod 11, which is why it sometimes ends in X. Both are computed correctly here.
What you can control
- Seven code standards, each with the right length and check-digit algorithm.
- ISBN-13 always starts with the 978 or 979 Bookland prefix, as real ISBNs do.
- A company prefix can be supplied so a batch shares a plausible manufacturer block.
- Hyphenation for ISBNs is optional, because catalogues and databases disagree on storing it.
What this is not
The check digits are valid but the codes are not registered with GS1 or any ISBN agency. A lookup against a product database will find nothing.
Questions
Why does an ISBN-10 sometimes end in X?
Its check digit is mod 11, which can produce a value of ten. The letter X stands in for it, since a single digit cannot.
Are these registered barcodes?
No. They pass check-digit validation without being assigned to any product. Scanning one into a real point-of-sale system will return no match.
What is the difference between UPC-A and EAN-13?
EAN-13 is UPC-A with a leading country digit. A UPC-A code is an EAN-13 with a leading zero, which is why the check digit calculation is the same for both.