A control circuit includes a plurality of drive current output circuits, a control voltage generating circuit, a first current output circuit, a second current output circuit, a voltage divider and a compensation voltage generating circuit. In one configuration, each mail piece includes a tracking code. The present invention discloses, among other things, transgenic mice carrying most of the human Ig Lambda light chain locus in their genome. The amount of light detected by the light detector depends on the proximity of each of the faces of the strip of material to ends of the optical fibers.