BAR CODE BASICS
Glossary of Terms
2 of 5: a one-dimensional, discrete, variable-length, numeric-only symbology in which each digit is represented by five bars, two of which are wide. Spaces are only used to separate bars, and carry no additional meaning in this symbology. (See also Interleaved 2 of 5).
3 of 9: (See Code 39.)
-A-
Alignment: the relative position of a scanner or light source to a bar code.
Alphanumeric: alphabetic and numeric.
ASCII: the American Standard Code for Information Interchange, a standard that identifies a set of 128 data characters for computer and data communication use and specifies the binary representation and meaning of those characters. Most desktop computers, bar code readers, and public data communication networks can use the ASCII character set. (See also EBCDIC and Full-ASCII).
Aspect Ratio: the ratio of height to width of a bar code symbol. A code twice as high as wide would have an aspect ratio of 2; a code twice as wide as high would have an aspect ration of ½ or 05.
-B-
Background: the area surrounding as printed symbol.
Bar: a dark element of a printed bar code symbol, usually formed by the inked area over a light background. (See Space and Reversed Bar Code.)
BarCode: a machine-readable “typeface” most commonly used for identification data. A printed bar code is made up of rectangular bars and spaces grouped in patterns that represent data characters, start/stop characters, and (optionally) check characters. A complete set of rules for constructing such a symbol, including the definitions of all patterns and check character calculations, is called a “symbology.”
BarCode Density: the number of characters that can be represented in a linear inch. (See also Density).
BarCode Reader: a device used to identify and read a bar code symbol.
Bar Length: the bar dimension perpendicular to the bar width.
Bar Width: the thickness of a bar measured from the edge closest to the symbol start character to the trailing edge of the same bar.
Bar Width Reduction: reduction of the nominal bar width dimension on film masters or printing plates to compensate for printing gain.
Bidirectional Read: the ability to read data successfully whether the scanning motion is left to right or right to left.
Bidirectional Symbol: a bar code symbol that permits reading in complementary (two) directions.
Bit: an abbreviation for “binary digit.” A single digit in a binary number.
-C-
CD (Charge-Coupled Device): a type of reader (named for the technology it uses to detect light) that can electronically “scan” reflected light from a bar code signal without the need for mechanical moving parts.
Character: a single group of bars and spaces that represent an individual digit, letter, or punctuation mark (a single keystroke on a computer keyboard).
Check Character: a character included within a symbol whose value is based mathematically on other characters included in the symbol. It is added to allow a mathematical check of the accuracy of the read.
Clear Area: (See Quiet Zone.)
Closed System: in the context of bar code systems, a system installed for a specific customer that is only used internally by that customer. A closed system is typically intended to meet only the individual customer’s requirements and, therefore, is not subject to industry or governmental standards governing symbology, formatting, etc. (Contrast with Open System.)
Codabar: a one-dimensional, discrete, variable-length symbology capable of representing the entire ASCII character set, and containing special compression techniques for efficiently codingsequences of numeric digits. Code 128 was specifically designed at the time to provide higherdensity (for a given X dimension) than most other codes.
Code 128: a one-dimensional, continuous, variable-length symbology capable of representing the entire ASCII character set, and containing special compression techniques for efficiently codingsequences of numeric digits. Code 128 was specifically designed at the time to provide higherdensity (for a given X dimension) than most other codes.
Code 16K: a stacked, two-dimensional symbology based on the same principles as Code 128, but designed for high-density printing and small label size requirements. A Code 16K symbol contains two to sixteen rows, separated by horizontal lines (to detect accidental scanning out of one row into the next).
Code 39: a one-dimensional, discrete, variable-length symbology capable of representing the digits 0-9; the letters A-Z; and the punctuation marks-, ., *, $, /, +, %, and a blank space. Sometimes called 3 of 9 because every data character is made up of nine elements, three of which are wide.
Code 49: a stacked, two-dimensional symbology designed of high-density printing and the labeling of small items. A Code 49 symbol contains two to eight rows, separated by horizontal lines (to detect accidental scanning out of one row into the next). The basic character set of Code 49 is similar to that of Code 39, and a related doubling technique is used to represent the full ASCII character set. A highly sophisticated compression scheme also allows very compact encoding of runs of numeric digits.
Code 93: a one-dimensional, continuous, variable-length symbology, which represents essentially the same data as Code 39 (including a full-ASCII option), but with higher density (for a given X dimension).
Contact Reader: a bar code reading device that must be placed in contact with the bar code in order to scan and decode it. (Manual devices that must be placed within a fraction of an inch of the bar code are also commonly referred to as contact readers.) (Contrast with Noncontract Reader.)
Continuous Code: a bar code symbology in which trailing space widths are part of the character patterns, and therefore may not vary. (Contrast with Discrete Code.) Continuous codes are normally printed from static film masters or with programmable printing devices (dot matrix, ink jet, laser printer, etc.)and not with mechanical numbering wheels.
-D-
Density: the amount of information that can be represented in a given areas of a form, document, or label. Density may be specified directly (as in “5.5 characters per inch”) or indirectly for a given symbology (as in Code 39 at 2.5-to-1 with an X dimension of 7.5 mils”).
Depth of Field: the range between the maximum and minimum distance from which a symbol can be read.
Discrete Code: a bar code symbology in which each character begins and ends with a bar element. The space separating the end of one character from the beginning of the next character (intercharacter gap) is not held to the same tolerances as the spaces within a character, and may usually “float” slightly without affecting the readability of the code. Therefore, continuous codes may be printed on press using mechanical numbering wheels.
-E-
EAN: the European Article Numbering code, the international standard symbology for retail packaging. EAN is a one-dimensional, continuous, numeric-only, fixed-format code. EAN is a “superset” based on the same design principles as UPC; EAN scanners can typically read UPC codes, but not visa versa. As with UPC, there are several defined formatting options; the most common are EAN-8 and EAN-13.
EBCDIC: the Extended Binary Coded Decimal Interchange Code, a standard that identifies a set of 256 data characters for computer and data communication use and specifies the binary representation and meaning of those characters (primarily used on mainframe computers). EBCDIC and ASCII specifications are different, therefore data must be translated when shared between devices that use these two standards. (See also ASCII.)
Element: an individual bar or space in a bar code.
Encoded Area: the total linear dimension consumed by all characters of a code pattern, including start/stop codes and data.
Extraneous Ink: ink in a scan area not intended to be there, e.g., tracking and splatter.
-F-
Film Master: a photographic film representation of a specific symbol from which a printing plate is produced.
First Read Rate: the percentage representing the number of successful reads per 100 attempts to read a particular symbol.
Fixed-Format Code: a symbology (or format option within a symbology) that specifies position and length for the data to be represented. For example, a UPCA symbol contains exactly twelve digits: one digit for “symbol system” (product type), five digits for manufacturer identification, five digits for product identification (within that manufacturer’s product line), and one digit used as a check character, (Contrast with Variable-Length Code.)
Font: a specific size and design of printer’s type. Some desktop publishing systems use the term “font” to refer to an entire typeface/style family.
Format: the geometric construction rules that define a particular bar code or symbol.
Full-ASCII: an option within Code 39 and Code 93 that uses character pairs beginning with %, $, /, and + to represent all possible ASCII character data, rather than just the basic 43 characters defined in Code 39 and Code 93. A related (though slightly different) technique is also used in Code 49.
-G-
Guard Bars: the alternating module pattern at both ends (bar-space-bar) and center (space-bar-space-bar-space) of a UPC/EAN Version A symbol, used in those symbologies to provide reference points for scanning. The complex character structure of UPC/EAN eliminates the need for more complex directional start and stop characters.
-H-
Helium Neon Laser: the type of laser most commonly used in bar code scanners.
-I-
Intercharacter Gap: the space between two adjacent bar code characters in a discrete code. An intercharacter gap is normally about one module wide, but is usually held to looser tolerances than the spaces within a character pattern.
Interleaved 2 of 5: a one-dimensional, continuous, numeric-only symbology based on 2 of 5 code. Digits are represented in pairs, where the first digit of the pair is encoded in five bars (two of which are wide)and the second digit of the pair is encoded in the adjacent five spaces (two of which are wide). Consequently, an Interleaved 2 of 5 symbol contains an even number of digits (zero-padding may be used for odd-length data). For a given X dimension, Interleaved 2 of 5 can represent numeric data at about twice the density of Code 39.
Interleaved Bar Code: a bar code in which characters are paired together using bars to represent the first character and spaces to represent the second.
-K-
Key Mark or Trigger: a printed graphic that indicates to the scanner that the code is in a position to be read; used in some fixed-beam readers.
-L-
Ladder Code: a code pattern presented in such orientation that the overall coded area from start to stop is perpendicular to the horizon. The individual bars appear as the rungs of a ladder.
Laser Scanner: an optical bar code reading device using a low-energy laser light beam as its source of illumination.
Light-Emitting Diode (LED): a semiconductor diode generally made from gallium arsenide that can serve as a near-infrared light source when voltage is applied continuously or in pulses.
Light Pen: a device that can detect a moving light beam on a CRT display and report its position back to a terminal or computer. This term is sometimes mistakenly used for a hand-held wand scanner, due to the similarity in the physical appearances of the two. (See Wand Scanner.)
-M-
Matrix Code: a two-dimensional code that represents information both by vertical and horizontal patterns. Examples include Vericode and Data Code. (See Two-Dimensional Code.)
Mil: 0.001 (one one-thousandth) of an inch, often used in specifying bar code dimensions. One mil is approximately 13.9 points. (See Substitution Error.)
Misread: a condition that occurs when the data output of a reader does not agree with the encoded data presented. (See Substitution Error.)
Module: the narrowest unit of measure in a bar code. A module may be “black” or “white.” Consecutive modules of the same “color” form bars or spaces that are wider than one unit.
Moving Beam Bar Code Reader: a device that dynamically searches for a bar code pattern by sweeping a moving optical beam through a field of view.
-N-
N: the ratio between wide elements and corresponding narrow elements (for bar codes using only two element widths).
No-Read, Non-Read, Non-Scan: the absence of data at the scanner output due to no code, defective code, scanner failure, or operator error.
Nominal Size: the standard size for a bar code symbol. Most codes can be used over a range of magnifications, commonly from 0.80 to 1.20 nominal.
Noncontract Reader: a bar code reading device that can detect light reflecting from a scanned bar code without requiring physical contact. Noncontact readers may have an effective scanning range and depth of field of a few inches up to a few feet, depending on the device. (Contrast with Contact Reader.)
Numeric: a machine vocabulary that includes only numbers as contrasted with alphanumeric, which includes both letters and numerals.
-O-
OCR-A: an abbreviation commonly applied to the character set contained in ANSI Std. X3.17-1974.
OCR-B: an abbreviation commonly applied to the character set contained in ANSI Std. X3.49-1975.
Offline: the operation of devices that are independent of a large central processing unit.
Online: an operation in which peripheral devices are connected directly to the computer central processor.
One-Dimensional Code: a symbology in which all information is represented only by the patterns of elements widths, independent of the perpendicular height of the bars. Examples include UPC, EAN, Codabar Code 39, Interleaved 2 of 5, Code 128, and Code 93.
Opacity: the property of paper that minimizes the show-through of printing from the back side or the next sheet. The ratio of the paper reflectance with a black backing to the paper reflectance with a white backing.
Open System: in the context of bar code systems, a system involving bar coded documents or materials that are transferred between companies or organizations. Participation in an open system typically means that the customer is required to utilize bar codes and readers that conform to industry or governmental standards. (Contrast with Closed System.)
Operating Range: the sum of the scanner’s optical throw and depth of field.
Optical Throw: the distance from the face of the code reader or scanner to the beginning of the depth of field.
Orientation: the alignment of bars and spaces to the scanner. Often referred to as vertical (picket-fence) or horizontal (ladder).
-P-
Parity Bar: added to a bar code to make the sum of all the bits (Parity Bar, Parity Module) always odd or always even for a fundamental check.
PDF417: a stacked, two-dimensional code designed for high-density encoding of large amounts of information (“PDF” stands for Portable Data File).
Picket-Fence Code: a bar code or symbol presented in such a manner that its overall length dimensions is parallel to the horizon. The bars are presented in an array that looks like a “picket fence.”
Point: a unit of measure used in printing, most often to specify type size or rule thickness. There are approximately 72 points per inch.
POS: an abbreviation for point of sale, signifying data entry systems where actual transactions are recorded by terminals operating on-line with a central computer. These systems frequently employ optical scanning as a means of capturing data.
Preprinted Symbol: a symbol that is printed in advance of application, either on a label or on the article to be identified.
PCS (Print Contrast Signal): a measurement of contrast (brightness difference) between the bars and spaces of a symbol. A minimum PCS value is needed for a symbol to be scanned. PCS values can be calculated and displayed automatically on suitable instruments.
Print Quality: the complete analysis of a printed symbol with regard to reflectance properties as well as symbol specifications.
-Q-
Quiet Area: (See Quiet Zone.)
Quiet Zone: a required clear space, containing nodark marks, that precedes the start character of a symbol and follows the stop character. Sometimes called “clear area.”
-R-
Read Area: the scan path or scan area
Reflectance: the amount of light returned from an illuminated surface.
Resolution: (1) the dimension of the smallest element that can be printed by employing a particular technique; (2) the narrowest element dimension that can be distinguished by a particular reading device.
Reversed Bar Code: bar code produced by printing space elements in opaque light color over a dark background. (See Bar and Space.)
-S-
Scan: the search for a symbol that is to be optically recognized. A search for marks to be recognized by the recognition unit of the optical scanner.
Self Checking: a bar code or symbol using a checking algorithm that can be applied to each character to guard against undetected errors. Codes that do not self-check may employ a check digit or other redundancy in addition to the data message.
Softstrip: a high-density, two-dimensional data code read with special motorized scanning equipment.
Space: a light element of a printed bar code symbol usually formed by the un-inked background between bars. (See Bar and Reversed Bar Code.)
Spots: the opposite of “voids”, spots are defects consisting of ink or dirt spots within the spaces or quiet areas of a bar code. Depending on size and orientation, scanning across a spot could make a wide space appear to be two narrow spaces separated by a narrow bar.
Stacked Code: a two-dimensional bar code containing multiple “layers”, each of which is constructed as a one-dimensional symbol representing a segment of the message encoded in the entire symbol. Typically the layers provide enough information to allow reconstruction of the entire message, regardless of the order in which the layers are scanned. Stacked codes may be read by modified rastering scanners or by multiple strokes of a hand-held wand. Examples include Code 49 and Code 16K.
Start/Stop Character: a bar code character that provides the scanner with start and stop reading instructions as well a code orientation. The start character is normally at the left-hand end of a picket-fence oriented code. The stop character is normally at the right-hand end of a picket-fence oriented code.
Substitution Error: a type of error in which characters are replaced by incorrect information. Substitution errors can result from mistakes in encoding, reading, or human operator keyboard entry. For example, mistyping the number “1234” as “1264” because of improper placement of fingers on a keyboard is a substitution error. Most check character schemes provide a degree of detection for substitution errors. In addition, most modern bar code symbologies are designed so that damage to a single character pattern renders it unreadable rather than making it appear to be a different but valid character.
Symbol: a complete, single printed bar code image meant to be scanned as a unit.
Symbol Length: the length of the symbol measured from the beginning of the quiet area adjacent to the start character to the end of the quiet area adjacent to a stop character.
Symbology: a distinct type of bar code defined by the patterns used to represent data and the rules for constructing complete symbols using those patterns. Examples include UPC, EAN, Codabar, Code 39, Interleaved 2 of 5, Code 128, Code 93, Code 49, Code 16K, and PDF417.
-T-
Three of Nine: (See Code 39)
Transposition Errors: a type of error in which characters are “swapped” within a single data item. For example, mistyping the number “1234” as “2134” is a transposition error. While common in manually keyed data, this type of error virtually never occurs in bar code reading.
Two-Dimensional Code: a symbology that represents information by elements that change both vertically and horizontally. (Contrast with One-Dimensional Code.) Multiple scans or a complete camera-like image is used to decode two-dimensional bar codes. Examples include Code 49, Code 16K, PDF417, Vericode, and Data Code. (See also Matrix Code and Stacked Code.)
Two of Five: (See 2 of 5 at the beginning of this glossary.)
-U-
UPC: the Universal Product Code, used in the United States for identifying manufacturer and product for retail sales items: the “grocery store checkout” bar code. UPC is a continuous, numeric-only, fixed format code (with several defined formatting options)and is used almost exclusively for retail packaging. (See also EAN.)
UPC-A: one of the two most common UPC formats, in which product type, manufacturer, individual product code, and a check digit are all explicitly represented.
UPC-E: one of the two most commonly used UPC formats; used to abbreviate some UPC-A symbols that contain “runs” of consecutive zeros.
-V-
Variable-Length Code: a symbology that does not specify exactly how many characters may be represented in a single bar code symbol (although upper limits on symbol lengths may be specified.)
Voids: the opposite of “spots”, voids are image defects consisting of un-inked areas within the bars of a bar code symbol. Depending on size and orientation, scanning across a void could make a wide bar appear to be two narrow bars separated by a narrow space.
-W-
Wand and Scanner: a hand-held, pencil-like wand that is “stroked” across a bar code symbol and serves as a contact reader.
Wedge Reader: a reading device designed to be connected to a keyboard or a communication port. Its purpose is to mimic keyboard data entry of scanned bar coded data so that software modifications are not needed to accept bar coded data.
-X-
X Dimension: the width of the narrowest bar and narrowest space in a bar code. (See Module.)
