Bar code technology has been helping businesses minimize data entry errors, speed processes, and reduce costs for over thirty years. The fact is, bar code systems work. Yes, some are configured better than others, some are easier to use, but even the most unusual application has reaped substantial return on investment in a reasonably short time frame.
This document is designed to introduce this very effective technology to potential new users. Written in non-technical language, it covers the components of a bar code label, scanning options, and a short glossary of common industry terms.
A bar code is a machine readable code consisting of a series of bars and spaces printed in defined ratios. Bar code symbologies are essentially alphabets in which different widths of bars and spaces are combined to form characters and, ultimately, a message. Because there are many ways to arrange these bars and spaces, numerous symbologies are possible. Common linear symbologies include UPC/EAN, Interleaved 2 of 5 (I of 5), Codebar, Code 39, and Code 128.
While each symbology is in some way unique, the composition of a complete message (bar code) is surprisingly similar regardless of the symbology used. For example, all bar codes are based on some “X” dimension. The “X” dimension is the narrowest bar or space in the bar code. Designated in “mils” (thousandths of an inch), symbology standards usually specify a minimum value “X” to insure compatibility between reading and printing equipment used in open systems.
The “X” dimension determines a bar code’s density. Density refers to the amount of information that can be captured in the bar code in a particular space, usually a linear inch. While not intuitively obvious, high density bar codes have low numbers (e.g., 5 mil) and low density bar codes have high numbers (e.g., 55 mil). This is because individual characters consist of some combination of bars and spaces that are each multiples of “X”. When “X” is small, the area required for each character is less than when “X” is large; thus the bar code can hold more per linear inch and is said to be of higher density. Similarly, increasing the width of the narrowest element (“X”) increases the space required for each character and reduces the number of characters per inch. Because the resulting code is often quite large, very low density codes are often associated with applications such as warehousing that require reading bar codes from a significant distance (3 to 30 feet).
All bar codes have start/stop characters that allow the bar code to be read from both left to right and right to left. Unique characters placed at both the beginning and end of each bar code, the stop/start characters provide timing references, symbology identification, and direction of read information to the scanner. By convention, the unique character on the left of the bar code is considered the “start” and the character on the right of the bar code is considered the “stop.”
Immediately preceding the start character and following the stop character is an area of no markings called the quiet zone. Because there is no printing in this area, a scanning signal is not produced, thus the term “quiet.” The quiet zone helps the scanner find the leading edge of the bar code so reading can begin. As a rule, the quiet zone should be ten times the “X” dimension or 1/4″, whichever is greater.
Putting all these components together, we get a complete bar code such as the one found below. Notice the leading quiet zone followed by a start character, data, a stop character, and a final quiet zone.
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