The first barcodes implemented worldwide were 1-D barcodes. These linear codes only contain alphanumeric data. Each character in the code represents something different about the product and a database provides information on what each character means.
In most cases, 1-D barcodes are read from
left to right. The widths of the spaces and bars relate to a specific character
in the barcode. A quiet zone or margin is the white space to the
left and the right of the barcode; this helps the reader to locate the barcode.
As a general rule, the margins should be at least seven to ten times of the
narrowest bar width in the barcode.
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All the other bars in the code are based off a ratio of the narrowest bar width.
For example, 2:1, 3:1, and 2.5:1 are common ratios that describe the width of
white spaces and black bars based on the starting point of the narrowest black
bar. Some barcodes also have a guard pattern. The guard pattern is at
the beginning and end of the barcode; this pattern tells the barcode reader
where the barcode starts and ends.
Common 1-D barcodes include but are not limited to: the GS1; UPC (Universal Product Code), which is common in retail and consumer goods; EAN in the European Union; and Code 128, which can describe any ASCII 128 character and is commonly used in logistics. Most of these barcodes include a check digit as part of its standard. The check digit is used to verify that the code is complete and not damaged or otherwise missing information; it does this by performing a mathematical operation on the data within the code.
Other 1-D codes, such as Code 39 (widely used by the military), POSTNET (used by the United States Postal Service),Codabar, and Interleaved 2 of 5 offer optional check digits. If there is no error correction built into the code, there will naturally be an increase in misreads. Pharmacode, which is used for the pharmaceutical industry, can be read both forward and backward. The drawback of this code is that it must be positioned the same way each time it is read, even with an vision-enabled reader.
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