The present invention provides a method for stabilizing an oral solid formulation containing a benzimidazole-based compound or a physiologically acceptable salt thereof. The driving member has a permanent-magnet motor provided with two terminals and an output member, which is rotationally driven by the permanent-magnet motor. The method makes a second preliminary register allocation attempt except using a less restrictive register set for the identified instructions. With this calibration result, the optical properties of a device under test measured using the first polarized lightwaves of the first amplitude and the second polarized lightwaves of the second amplitude can be determined with reduced uncertainty due to intrinsic optical characteristics of the interferometric optical network analyzer.