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The last digit that tests the others.
Also known as: ISBN checksum, Book number check character
The final character of an ISBN, computed from the preceding digits to detect transcription error.
Detects transcription errors in an ISBN by a weighted sum over the preceding digits.
Contexts: Public information
Weights the digits by position, which catches transposed pairs as well as single wrong digits — the two commonest errors when a number is copied by hand.
Contexts: Public information
Uses the letter X for a check value of ten in the ten-digit form, which is why some ISBNs end in a letter and no other position ever does.
Contexts: Public information
A final digit, or the letter X standing for the value ten, printed at the end of the number and reproduced in the barcode.