A switching unit, equipped with a plurality of port cards and a plurality of switch cards connected in a non-parallel fashion to the port cards. An analog-to-digital converter is connected to the input pad for providing a numerical value of the externally generated analog signal, and is connected to the pre-sampling circuit for providing a numerical value of the internally generated analog reference signal. The band-pass filter absorbs a component of the light, in which a wave-length of the component of the light is no more than 440 nm, and the band-pass filter is arranged between the light source and the viewer. An innovation sequence is determined based on the prediction error and an index is selected based on the innovation sequence.