Method and device for checking patterns (1) disposed on a material strip (30) which patterns (1) consist of groups of dark and light areas (2,2*,3,3*) succeeding in the travelling direction (v) of the material strip (30) and the checking respectively, by displacing the position of the dark areas (2,3) and/or the light areas (2*,3*) of one group with respect to a related detector (8,9) in regard to the dark areas (2,3) and/or light areas (2*,3*) of another group with respect to another related detector (8,9) by detecting the existence or non-existence of dark areas and/or light areas and by creating a sequence of output signals dependent on the result of the detection by combining the output signals comprising information concerning said dark or light areas (2,2*,3,3*) of each detector (8,9) with the output signals depending on the detection of one of said dark or light areas (2,2*,3,3*) of the other detector (8,9) in a predetermined way by for example alternately activating each detector (8,9) by the other detector (8,9) and by comparing this sequence of output signals with a predetermined sequence of signals.
A bar code symbology comprises a set of symbols having characters and patterns of bars and spaces. Each character spans a distance of m module widths and is represented by n bars and p interleaved spaces. The largest single bar or space is limited to k modules in width. A human recognizable graphic element is included among the patterns of bars and spaces. At least a portion of the graphic element is machine readable and recognizable by a decoder as a portion of the symbol.
