This article evaluates an old and little used method, which involves holding a small light in front of the lens and marking the spot where the centers of the images reflected from the front and rear surfaces overlap. The location of the center found this way correlates very well with the marking lensometer method. This method may also be used while the patient is wearing the spectacle. Thus, the examiner may easily see the patient's pupillary center and the optical center simultaneously. Induced prismatic effects from inaccurate lens centering can easily be diagnosed without removing the spectacle from the patient's face.