on the bar code symbol 2 is substantially smaller than the smallest width of one line element 2a b the transmitted light beam 8 is amplitude modulated as shown in fig3 b by the reflection from the bar code symbol 2 in the event that no distortions or skewings of the received signal take place in the receiving element 4 the curve course shown in fig3 b corresponds to the received signal present at the output of the receiving element 4 the determination of the width of the individual line elements 2a b of the bar code symbol 2 in the evaluation unit 5 is suitably done by the turning point process in a first step the received signal is differentiated fig3 c next the extremes of the differentiated received signal are determined which correspond to the turning points of the received signal these turning points in turn define the transitions from a black to a white line element 2a b and vice versa to determine the turning points of the received signal the differentiated received signal is converted with preferably two switching thresholds s 1 and s 2 fig3 c into a binary signal train fig3 d the duration of the states 34 0 34 and 34 1 34 of the binary signal train is a measure for the width of the line elements 2a b of the bar code symbol 2 the duration of the states 34 0 34 and 34 1 34 can be detected in a simple way via a clock controlled counter as the diameter of the transmitted light beam 8 becomes greater or with increasing signal distortions in the receiving element 4 the edge errors also become greater that is the turning points of the received signal no longer coincide with the location.