Symbology Characteristics - Hand Held Products Quick Check Bar Code Verifiers 800 User Manual

Symbology Characteristics

Your Quick Check 600/800 Verifier can handle bar code symbologies with a
variety of characteristics. To help understand symbologies, you should be
familiar with the following commonly used terms:
• Code refers to the actual data contained in the bar code symbol, such as a
part number, serial number, transaction code or other type of data.
• Symbol refers to the actual arrangement of parallel bars and spaces that
encode the data.
• The character set describes the range of data characters that can be
encoded in a given symbol. For example, UPC uses only
numbers and is called a numeric symbology, whereas Code 39 uses
alphabetical characters, numbers and special characters.
• There are two symbology types, discrete and continuous.
• In a discrete code, each character stands alone and can be decoded.
Between characters is a loosely toleranced intercharacter gap which
contains no information. Every discrete character has a bar on each
end. One example of a discrete code is Code 39.
• In a continuous code, there are no intercharacter gaps. Every
character begins with a bar and ends with a space. The end of one
character is indicated by the start of the next
character. An example of a continuous code is UPC.
• The bar and space widths can vary within or between symbologies;
those with only two-element widths (wide and narrow) versus those
that use multiple widths.
• Two-width symbologies, such as Code 39, have a ratio of wide to
narrow typically between two and three.
• Multiple-width symbologies, such as UPC, allow the bars and
spaces to assume more than two different widths. Most multiple-width
symbologies have characters whose length is subdivided into a
predetermined number of modules. In addition, the width of each bar
or space is always an integral number of modules.
Bar code symbologies vary on the amount of information that can be encoded in
a given length. Usually, only characters have a specified density, since the
overall length of a symbol must include other characters. These other characters
may include a start/stop code and a check character.
• A start code is a pattern of bars and spaces that appears at the beginning of
a symbol to inform the reading tool where the symbol begins.
• A stop code is a pattern placed at the end of a symbol for marking the end of
the data characters. Sometimes the start and/or the stop characters also
indicate the scanning direction.
Quiet zones are areas at the beginning and end of a bar code symbol that allow
the optical equipment to differentiate a bar code from other printed material.
Most of the symbologies in use today are bidirectional; this means that they can
be read by a scanner either left-to-right or right-to-left without affecting the
decoded data.
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