The OCB100-KIT can also detect the difference between two semi-transmissive materials, such as in a label printer where a sensor is required to see through the liner of a roll of labels, but detect the label. A sample label and liner is included in the kit. To use the sensor for this application, set the load resistor to 9.6 K ohms by moving the shorting bar between pins 2 & 3. Next, place the labels in the center of the optical path and calibrate the sensor. Now move the labels back and forth in the gap to see that the green LED lights when the labels are present, but does not light when the label is not present. Remove the label / liner from the gap completely. The blue LED on the board should now be lit. A similar scheme is utilized to detect single or double feed checks in check scanners.