MSI Plessey (also known as just MSI or Modified Plessey) is a numeric-only barcode developed by MSI Data Corporation in the 1970s. The symbology is based on the Plessey barcode, which was introduced in 1970 by the Plessey Corporation in England. Today, Plessey itself is rarely used and not well supported. Even the specification for it is difficult to find (as only printed copies exist).
MSI Plessey can only encode the digits 0 through 9 and includes both a stop and start character. The symbology is variable length with the only limit on length being the width available for print.
MSI Plessey is a linear, one-dimensional (1D) barcode. This means the barcode is composed of a single set of varying-width vertical lines (black) and spaces (white). The data in the barcode is represented linearly by these black/white patterns (also called bars/spaces). Below is a simple example.
The symbology is further characterized as a continuous barcode; that is, there is no inter-character space between adjacent data characters. The space between characters is part of the data representation.
Like other, early numeric symbologies (e.g., Code 11) MSI is considered a weak or insecure symbology as a single print or read error can result in a misinterpreted character. To combat this, either a single or two-character check digit is often used, though not required. In the preceding example, the last digit (6) is actually the computed modulo 10 check digit for the data message (4321). Use of modulo 10 check digit is most common, though modulo 11, modulo 1010 (two modulo 10 check digits), and modulo 1110 (a modulo 11 check digit plus a modulo 10 check digit) are used as well.
Here is our example again, diagramed for clarity:
Who uses MSI Plessey?
MSI Plessey (and its predecessor, Plessey) were used in libraries, though this use has greatly diminished (Codabar is now more common). Today, the most common use of MSI Plessey is on retail shelves for inventory control.
The Cognex Mobile Barcode Scanner SDK supports MSI Plessey detection, enabling developers to gather relevant workflow and application data. You can download the SDK for free by registering on the Cognex Mobile Barcode Developer Network. In addition, the Barcode Scanner SDK supports a broad range of symbologies to meet your growing development needs.