A
barcode (or bar code) symbol, like a Universal Product Code (UPC), consists of patterns of black vertical bars with white spaces and numbers at the bottom of the symbol. Together these bars make up the symbology of the code. The thickness of the bars and the distance between them define the numbers contained in the bar code. A set of two black bars appear at the beginning, middle and end of the symbology and are called guard patterns. These patterns provide start and stop signals to tell a scanner where it is reading within the code. (Illustration: The UPC code for ketchup.)
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