A printed sheet product comprises a thin core having a pair of opposing major planar sides. A plurality of sets of code fields are printed on a first side of the core. Each set of code fields is printed with a numeric code unique to the set. At least a first code field of each code field set is printed...http://www.google.es/patents/US4978146?utm_source=gb-gplus-sharePatente US4978146 - Method for making uniquely encoded transaction cards and related sheet products
Method for making uniquely encoded transaction cards and related sheet products
