A method for the selective reduction of an aromatic compound. The cage is engaged with the housing, the cage and the housing together define a slot, and an entrance of the slot is adjacent to the front side so as to allow an electronic card to enter into the slot along a card insertion direction. While changing an offset code that is fed to an offset control input of the comparator, and while applying a fixed voltage level that represents a symbol in the transmission line analog signal, a value of the offset code which causes the output of the comparator to change states is captured.