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For instance, the UPC-A barcode for a box of tissues is "036000241457". The last digit is the check digit "7", and if the other numbers are correct then the check digit calculation must produce 7. Add the odd number digits: 0+6+0+2+1+5 = 14. Multiply the result by 3: 14 × 3 = 42. Add the even number digits: 3+0+0+4+4 = 11.
The check digit is computed as follows: Drop the check digit from the number (if it's already present). This leaves the payload. Start with the payload digits. Moving from right to left, double every second digit, starting from the last digit. If doubling a digit results in a value > 9, subtract 9 from it (or sum its digits).
The Luhn mod N algorithm generates a check digit (more precisely, a check character) within the same range of valid characters as the input string. For example, if the algorithm is applied to a string of lower-case letters (a to z), the check character will also be a lower-case letter. Apart from this distinction, it resembles very closely the ...
A UPC barcode. The Universal Product Code (UPC or UPC code) is a barcode symbology that is used worldwide for tracking trade items in stores.. The chosen symbology has bars (or spaces) of exactly 1, 2, 3, or 4 units wide each; each decimal digit to be encoded consists of two bars and two spaces chosen to have a total width of 7 units, in both an "even" and an "odd" parity form, which enables ...
The check digit is a weighted modulo-103 checksum. It is calculated by summing the start code 'value' to the products of each symbol's 'value' multiplied by its position's weight in the barcode string. The start symbol and first encoded symbol are in position 1. The sum of the products is then reduced modulo 103.
The barcode scheme does not contain a check digit (in contrast to—for instance—Code 128), but it can be considered self-checking on the grounds that a single erroneously interpreted bar cannot generate another valid character. Possibly the most serious drawback of Code 39 is its low data density: It requires more space to encode data in ...
Because digits are encoded by pairs, only an even number of digits can be encoded. Typically an odd number of digits is encoded by adding a "0" as first digit, but sometimes an odd number of digits is encoded by using five narrow spaces in the last digit. [a] A checksum can be added as last digit, which is calculated in the same way as UPC ...
Because Codabar is self-checking, most standards do not define a check digit. [3] Some standards that use Codabar will define a check digit, but the algorithm is not universal. For purely numerical data, such as the library barcode pictured above, the Luhn algorithm is popular. [4] When all 16 symbols are possible, a simple modulo-16 checksum ...