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Since the result is zero, the message is considered to be valid, so the reader
outputs the message: 0123456
2-1-2-1 Weighted Modulo 10 Check Character
Starting with the check character and working backward through the message,
the image scanner applies a multiplier of 1, then 2, then 1, then 2, and so on.
When the result of the multiplication is greater than 9, add both digits to the run-
ning sum. This is often referred to as the LUHN formula. One common applica-
tion of the LUHN formula is validate credit card numbers. This is the modulo 10
checking scheme used in MSI Code and in Code 32 Pharmaceutical (PARAF).
To apply this weighting scheme, set the OCR check character to
"0123456789x2x1" or scan the following symbol:
Example: Scan the 2-1-2-1 Weighted Modulo 10 Check Character symbol. Also
enter the OCR template:
ddddddc
Then scan the string below:
0128454
The reader performs the check character computation below:
(0 x
1 + 1 x 2 + 2 x 1 + 8 x 2 + 4 x 1 + 5 x 2 + 4 x 1) modulo 10
= (0 + 2 + 2 + (1 + 6) + 4 + (1 + 0) + 4) modulo 10
= 0
Since the result is zero, the message is considered to be valid, so the reader
outputs the message: 012845
OCR ISBN Application Example
One application of OCR is to read the ISBN characters typically encoded using
the OCR-A or OCR-B font. This is especially useful when the ISBN number is
not encoded in an EAN-13 barcode. The following example shows how to con-
figure the image scanner to read the ISBN strings on books in Japan. After you
2-1-2-1 Weighted Modulo 10
Check Character