Plessey is a linear 1D barcode. The MSI Plessey Code is is a pulse-width modulated non-self checking code. Each character is represented by 4 bars; a narrow bar represents a binary 0 and a wide bar represents a binary 1. The bars have the binary weights 8-4-2-1. It is possible to encode the digits 0 through 9 and the letters A through F, although this code is most often used just for numeric information. The start character is a single wide bar, and the stop character is two narrow bars.