About Plessey Barcodes
Plessey is a legacy 1D linear barcode symbology developed in 1971 by the Plessey Company in the United Kingdom. It was one of the earliest barcodes used in retail inventory and shelf marking, paving the way for modern retail codes like EAN and UPC. Plessey encodes numeric digits and hexadecimal letters (A-F), representing a transitional step in early barcode technology. It is a continuous, self-checking symbology that uses a cyclic redundancy check (CRC) for error detection.
How Plessey Encoding Works
Plessey encodes digits 0-9 and letters A through F. Each character is represented by four bars and spaces, with the width of the bars and spaces determining the binary value (0 or 1). Plessey barcodes end with an 8-bit checksum calculated via a CRC-8 polynomial algorithm. This CRC provides excellent security against scanning errors. The barcode structure starts with a start character, followed by data, CRC bytes, and a stop guard pattern.
Common Applications and Industries
Plessey was widely used in UK libraries, retail warehousing, and department stores in the 1970s and 1980s. In the United States, it was adapted into the MSI Plessey barcode. Today, the original Plessey barcode is rare, having been replaced by EAN-13, UPC-A, and Code 128. However, it is still supported by multi-protocol barcode scanners to maintain compatibility with legacy archival materials and library catalogs.
Advantages & Limitations
Plessey features an advanced CRC-8 checksum, providing very high resistance to scanner errors. It also supports hexadecimal characters (A-F), which was a unique feature among early linear barcodes. The downside is its low data density and lack of uppercase/lowercase letter support, making it obsolete for modern logistics that require alphanumeric encoding.