Abstract
The essential requirement demanded of a code mark printer is that it should produce economically an easily readable code pattern on letter mail of different surface colours and textures, accurately and without smudging or defacement of written matter. The merits of various methods of marking are compared and reasons for the choice of phosphor for letter mail explained. The advantages and disadvantages of possible coding techniques are discussed. Properties of the phosphor carriers are closely related to the printing method adopted. Printer mechanisms designed for hot transfer from coded tape are described, including three production models in service. The method of marking to permit identification of the source of coding, which is necessary for investigations into mis-routing, is described. The paper concludes with a history of experience to date and comments on possible future developments.
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