Composition
Each UPC-A barcode consists of a scannable strip of black bars and white spaces, above a sequence of 12 numerical digits. No letters, characters, or other content of any kind may appear on a standard UPC-A barcode. The digits and bars maintain a one-to-one correspondence - in other words, there is only one way to represent each 12-digit number visually, and there is only one way to represent each visual barcode numerically.
The scannable area of every UPC-A barcode follows the pattern SLLLLLLMRRRRRRE, where the S (start), M (middle), and E (end) guard bars are represented exactly the same on every UPC and the L (left) and R (right) sections collectively represent the 12 numerical digits that make each UPC unique. 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. The non-numerical identifiers, the guard bars, separate the two groups of six digits and establish the timing.
| Standard UPC-A | GTIN-12 number encoded in UPC-A | Standard UPC-E* |
|---|---|---|
123456 789999 |
1 23456 78999 9 |
234569 |
- Note: UPC-A 123456789999 corresponds with UPC-E 234569 (with the EOOEOE parity pattern). Equivalent UPC-A and UPC-E barcodes share the same check digit, which is 9 in this case.
Read more about this topic: Universal Product Code
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