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
Famous quotes containing the word composition:
“There was not a grain of poetry in the whole composition of Lord Fawn, and poetry was what her very soul craved;Mpoetry, together with houses, champagne, jewels, and admiration.”
—Anthony Trollope (1815–1882)
“I live in the angle of a leaden wall, into whose composition was poured a little alloy of bell-metal. Often, in the repose of my mid-day, there reaches my ears a confused tintinnabulum from without. It is the noise of my contemporaries.”
—Henry David Thoreau (1817–1862)
“The naive notion that a mother naturally acquires the complex skills of childrearing simply because she has given birth now seems as absurd to me as enrolling in a nine-month class in composition and imagining that at the end of the course you are now prepared to begin writing War and Peace.”
—Mary Kay Blakely (20th century)