<convention> A printed horizontal strip of vertical bars of varying widths, groups of which represent decimal digits and are used for identifying commercial products or parts. Bar codes are read by a bar code reader and the code interpreted either through software or a hardware decoder.
All products sold in open trade are numbered and bar-coded to a worldwide standard, which was introduced in the US in 1973 and to the rest of the world in 1977. The Uniform Code Council in the US, along with the international article numbering authority, EAN International, allocate blocks of unique 12 or 13-digit numbers to member companies through a national numbering authority. In Britain this is the Article Number Association. Most companies are allocated 100,000 numbers that they can use to identify any of their products, services or locations.
Each code typically contains a leading "quiet" zone, start character, data character, optional check digit, stop character and a trailing quiet zone. The check digit is used to verify that the number has been scanned correctly. The quiet zone could be white, red or yellow if viewed by a red scanner. Bar code readers usually use visible red light with a wavelength between 632.8 and 680 nanometres.
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