Barcode Guide

Glossary of Barcode Terms

This page lists definitions for commonly used terms that are relevant to the automatic identification and data capture (AIDC) industry as a whole and barcode symbologies in particular.

bearer bars. Optional bars that constitute either a frame around an Interleaved 2 of 5 symbol or two bars across the top and bottom of the symbol. Historically, they were a byproduct of the printing process, but they can also be used to prevent scanning errors.

bidirectional. Able to be decoded when scanned from left to right or from right to left.

check digit. One or more extra characters that are appended to a barcode symbol in a type of redundancy check that is used for error detection. Their values are derived by an algorithm from the sum or weighted sum of the other characters in the data stream.

checksum. See check digit.

code set . A subset of the full ASCII character set that is used in Code 128 and its variants. A symbol can switch between code sets by using control or flag characters.

color field. A optional block of color that can be placed along one or more sides of the Data Matrix portion of a 2D-Pharmacode symbol. Color fields are used to check for the presence of certain colors on pharmaceutical packaging (such as red warning labels).

continuous. Having no intercharacter spaces. In a continuous barcode, the end of one character is indicated by the beginning of the next, with no gap between.

correction level. See error correction.

cyclic redundancy check (CRC). A method of error detection that uses a polynomial calculation to compare the encoded check value with the calculated check value. If the CRC check values do not match, then the code contains a data error.

data layer. In the Aztec Code symbol, a two-module-wide row of data and correction characters that wraps clockwise around the central finder pattern. Each data layer begins immediately beside the ending edge of the preceding layer and ends beside its own starting edge. As a result, a barcode scanner can read the data layers as a continuous spiral.

direct parts marking (DPM). A variety of processes that are used to mark barcode symbols directly on a part rather than on a label, frequently used in manufacturing industries. Techniques include laser engraving, chemical etching, and dot peen marking.

discrete. Having intercharacter spaces. In a discrete barcode, each character stands alone and is separated from the next by an intercharacter space or gap.

error correction. A means of preserving data integrity in symbols that encode large amounts of information by encoding redundant information into the symbol. When error correction is used, the scanner can detect and correct any missing information (as might occur if the symbol is damaged). Various levels of correction can be used; the higher the correction level, the more redundant information is encoded, and the more robust (error-proof) the symbol is. However, higher correction levels have the consequence of lessening the data-carrying capacity of the symbol.

G dimension. The distance between the imaginary grid lines that form the spacing baseline of a PosiCode symbol. The bars are centered on these grid lines, and the data is encoded by using the width of the spaces between bars.

guard bar. A start, stop, or center character. In the UPC/EAN family, guard bars are longer than the other bars in a symbol. They are sometimes called security bars.

human readable interpretation. The numbers and letters that appear below a barcode symbol, which correspond to the data that is encoded in the symbol. The human readable interpretation makes it possible for a human operator to enter data manually in the event of a scanner misread.

intercharacter space. A narrow space (usually one module wide) that separates each barcode character from the next but is not itself a part of a barcode character. These spaces are found in discrete symbologies and are absent in continuous symbologies.

mask. In some two-dimensional barcodes, an easier-to-read symbol that is overlaid on a harder-to-read symbol to reduce scanning errors. The data in the mask is mapped to the original data.

module. The smallest element in a barcode symbol. A module has a width, height, or diameter that is equivalent to the X dimension of the barcode.

modulo. Sometimes shortened to "mod." A calculation that is used to find the check digits for a barcode symbol; this calculation is based on a particular number, such as 10. For example, a simple modulo 10 calculation sums the digits that are encoded in the symbol and then appends the check digit that makes the digits add up to a multiple of 10.

omnidirectional. Able to be decoded when scanned from any direction.

quiet zone. The blank space that surrounds a barcode symbol; required by most symbologies for accurate scanning.

Reed-Solomon error correction. A method of non-binary cyclic error correction that can detect and correct multiple symbol errors and erasures. It is widely used in 2-D symbologies.

security bar. See guard bar.

self-clocking. Having the inherent ability to give scanners the reference information they need to measure the relative positions of all the barcode elements without requiring a separate clocking track. All modern symbologies are self-clocking.

separator bar, separator pattern. A row of contrasting modules that appears between the stacked rows in a 2-D stacked or composite symbology, such as GS1 DataBar Stacked. The separator pattern starts and ends with a four-module-wide space. Where the top row and bottom row modules that are vertically adjacent to a separator pattern module have the same color, the separator module is the opposite color. Where the top row and bottom row modules have different colors, the separator module is the opposite color to the separator module to the left. In a region that has complementary top and bottom row colors, this results in a pattern of alternating one-module-wide bars and spaces.

start character, stop character. A particular pattern of lines and spaces in a linear symbol that is placed at the beginning and end of the symbol to indicate the scanning direction, beginning and end of the data sequence, and sometimes the symbology version.

trigger mark. An optional feature of the 2D-Pharmacode symbol; consists of a combination of bars and spaces that enables scanning to be synchronized automatically on fast-moving items (for example, items on a conveyor belt).

X dimension. The nominal dimension (height, width, or diameter) of the smallest element in a barcode symbol. It is often expressed as multiple, as in 1X or 10X.


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