| 摘要 |
The control element has a first drawing printed on a first side of the article, comprising at least a first set of geometrical shapes. It includes a second drawing printed on a second side of said article, the second drawing being printed so as to face the first drawing and be in register with the latter, said second drawing comprising at least a second set of geometrical shapes corresponding to the first screen. At least one of said geometrical sets includes sectors which are offset so that, when the front side/reverse side register is correct, the control element has regions of variable density which are visible in transmitted light and are created by said offset sectors.
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