Plessey

Plessey was a British-based international radio, electronics and telecommunications company. Founded in 1917 in Marylebone, central London but moving to Cottenham Road in Ilford early in 1919 (and then to Vicarage Lane where it remained) it became one of the largest manufacturers in this field as the radio and television industries grew.

Plessey were partners in the development of the Atlas Computer in 1962 and in the development of Digital telephone systems - System X - during the late 1970s. The company was taken over in 1998.

Plessey is also a name for a barcode symbology developed by them, which is still used in some libraries and for shelf tags in retail stores, in part as a solution to their internal requirement for stock control. Its chief advantages are the relative ease of printing using the dot-matrix printers popular at the time of the code's introduction, and its somewhat higher density than the more common 2 of 5 and 3 of 9 codes.

Plessey barcodes use two bar widths. Whitespace between bars is not significant. The start element is a wide bar, and the stop element is two narrow bars. In between, the bars are in groups of four. High order bars appear leftmost. Narrow bars are zero and wide bars are 1.

This symbology is not self checking, though a modulo 10 or modulo 11 checksum (depending on application) is usually appended.