A barcode symbol appears as alternating black vertical bars with white spaces. The numbers at the bottom of the barcode symbol (called the human readable) represents the data encoded in the symbol. The numbers are made “machine readable” (able to be read by the barcode scanner) by representing the numbers by groups of different thickness bars and spaces. Special sets of bars provide start and stop signals to tell a scanner where it is reading within the barcode.
The data in the Universal Product Code or U.P.C. (the barcode that appears on grocery and other point of sale items) is encoded in the bars and spaces in a very specific way. There are three elements to this “data string” in U.P.C. barcodes:
- A company prefix - this is the globally unique GS1 Company Prefix assigned to your company by GS1 US. It ensures that your product’s barcode is not confused with another company’s product.
- An item reference - the item reference number is assigned by your company. The GS1 Company Prefix plus the item reference number totals 11 digits.
- A check digit - A special formula using the other 11 digits is used to calculate the check digit. This 12th digit ensures the accuracy of the information in your barcode when it is scanned.