As market conditions descend or ascend an axis of prices, the display of market information is repositioned, at a pre-determined rate if desired, around an item of interest. The other processors enter the debug mode as a result of the one processor asserting a debug event signal upon initially entering the debug mode. Labels 12c on the recording medium 12a can always be detected by either or both the reflection photosensor 26 and the transmission photosensor 27.