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MSI Plessey is a numeric, variable length symbology originally developed
by the Plessey Company of England in the early 1970s. However, the most
widely supported version, "MSI" Plessey, is currently maintained by Symbol
Technologies, Inc.
Like Interleaved 2-of-5 and UPC, Plessey is an all-numeric language.
It has an interesting simplicity in that the bar code pattern for each
character is a simple binary pattern of "zeros" and "ones" that directly
represent the given number. Accordingly, with casual familiarity with the
code, you can actually read the bar codes with your eyes. However,
Plessey does not encode numbers efficiently, and other characteristics of
the language make it one of the most error-prone of all bar code languages.
Accordingly, the MSI company came out with a revised standard for the
Plessey language (now called MSI Plessey) which employed a second check
digit. This improved the reliability of the language enough so that the
MSI version of the code has continued in use in specialty applications.
Although Plessey was originally developed for use in the library industry,
its use in libraries is now quite rare. Today, MSI Plessey is the most
common bar code language used for inventory tracking on the shelves in
supermarkets. While MSI Plessey is not actually used on the products
themselves (which contain UPC codes), it is used on the front edge of
the shelves to indicate where each product is stored.
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