This European Standard specifies optical characteristics for processing letters and gives guidelines on the values of these attributes that will assure a high level of address readability. It is aimed at facilitating relations between Postal Operators and Customers by providing information that mailers can use to ensure that the addresses they print can be processed successfully by postal automation systems. The standard is intended to support: - assessment of the probable readability of a printed address, using given address recognition equipment, without actually submitting it to the equipment; - determination of the changes in address printing characteristics that are required to achieve a desired level of address readability using given address recognition equipment; - assessment of the complexity, and thus the cost, of the address recognition equipment needed to achieve a desired level of readability of addresses with given printing characteristics. The standard applies to mail items whose size is up to and including C5 1 , but may also be applied to oversize items, commonly referred to as C5+, and to flats. The address blocks covered are: - the delivery address block; - the sender address block if this is printed on the same side of the mail item as the delivery address block. The guidelines provided in the standard apply to address blocks as they appear on finished mail items when submitted to postal operators, and not just to addresses and the substrate on which they are printed. Users of the standard are responsible for determining the physical parameters which are required to achieve compliance after taking account of characteristics which result from mail item features, other than printing, such as covering, the use of transparent window envelopes and the use of address labels. The guidelines are based on physical attributes that tend to influence the readability of addresses by optical character recognition (OCR) equipment and by video-coders.