MSI-PLESSEY is a variable length, numeric only, symbology. The symbology is one of the earliest barcode symbologies ever developed and is based on a four bit binary number scheme. Each symbol is framed by a start and a stop pattern and contains a check character that is calculated from the values of each of the encoded data digits. MSI-Plessey is rarely used in anything other than grocery store shelf marking applications. In fact most modern barcode readers do not provide support for reading MSI-Plessey symbols.