An apparatus and method for performing a light absorption measurement and the compliance measured for the reference sample to the test sample is disclosed. The invention method, by moving the reference sample container carrier of the device, to direct the light along the optical path to a first reference sample containers accommodated in the carrier phase, the detection system from the illumination system is located on the second position on the optical path, the method comprising performing a light absorption measurement on the first reference sample from the second location, the method comprising: off position the first reference sample containers by moving the carrier from the optical path, the light of the test sample container in the testing of the device the sample container holder path phase in which the second position and is in accordance with the steps, and the light path placed in the first position of the different positions to direct the light comprising the step of performing a light absorption measurement on the test sample in the test sample container in a first position do.