An apparatus for determining spherical and cylinder components of subjective refraction of a patient’s vision includes a wavefront measurement device that can produce a measure of quality of vision in a return beam from the patient’s eye viewing a target through a corrective test lens in the apparatus. During use, the observed usage of the device is compared to an expected pattern of usage of the device. The image taking unit takes a second image of a target object. In this method, a leakage current associated with leaky circuits in the charge pump can be determined. This transformation is transparent to the designer of the business application.