The UPC has only numerals (digital number), without letters (such as ‘A’, ‘B’,… ) or other (control / function ) characters.
Total 12 decimal digits, its format/syntax is:
SLLLLLLMRRRRRRE
In which:
- S – Start, E – End
fixed bit pattern 101
- M – Middle
fixed bit pattern 01010, called guard bars
- L – Left, R - Right
both have 6 digits, each digit is a 7 bits code
So, total bits = S + L + M + R +E = 3 + 7 * 6 + 5 + 7 * 6 + 3 = 95 bits
Since S, M, and E all include two bars, and each of the 12 digits of the UPC-A barcode consists of two bars and two spaces, all UPC-A barcodes consist of exactly (3 × 2) + (12 × 2) = 30 bars.
For left digits and right digits:
The first digit L is the prefix.
The last digit R is an error correcting check digit, allowing some errors in scanning or manual entry to be detected.
UPC data structures are a component of GTINs (Global Trade Item Numbers). All of these data structures follow the global GS1 standards.
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| 1.4. Example |  | 1.5.1. Bit Pattern of Digit |
