A-2
CELL-DYN
3000 System Operator’s Manual
9140240E — May 1995
Bar Codes
Appendix A
Understanding the Label “Code”
In all bar code symbologies, the code consists of elements (single bars or
white spaces) and characters (groups of elements which stand for
numbers or letters). For example, in Code 39, a widely used symbology,
each code character contains nine elements, at least three of which must
be wide. Wide elements (whether they are bars or spaces) in this
symbology have a binary value of 1. Narrow elements have a binary
value of 0.
Most contemporary bar code systems have several features in common.
These include:
•
The quiet zone, an area immediately before and after the bar code
symbol, which enables the scanner to read the code properly.
•
Start and stop characters which indicate the beginning and end of
the bar code symbol. They allow the label to be scanned from either
right to left or left to right, ensuring that code information is
transmitted correctly.
•
Intercharacter gaps that act as “spaces” between each character in
the bar code symbol. Code 39 contains these gaps, but other codes,
including Interleaved 2 of 5, do not use them.
•
The interpretation line, an area at the bottom of the bar code label
where human-readable information can be placed. This may or
may not be the same data as in the label code.
•
The optional check digit, an extra character in the bar code which
permits the scanning device to mathematically determine whether
it read the code correctly. This keeps the error rate as low as one in
every billion characters read.
Bar Code Types and Characteristics
The Sample Loader reads three symbologies of bar codes, the
descriptions of which follow:
Code 39
Also referred to as code 3 of 9, Code 39 encodes 43 data characters: 0-9,
A-Z, six symbols and spaces. Each character is represented by nine
elements, three of which are wide and six of which are narrow.
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