Abstract: An optical storage carrier is provided with an entrance face, and information layer and a transparent layer between the entrance face and the information layer. The information layer holds a relief structure representative of readable data that may be read through the transparent layer by focusing of radiation beam. The carrier also includes a read-only zone such as the conventional lead-in zone where informative data is stored indicating at least one radius where a thickness variation of the transparent layer potentially occurs. When inserted in a scanning device, a measurement is carried out of the thickness of the transparent layer at the indicated radius and appropriate spherical aberration correction can be derived and the focus of the light beam on the information layer is adjusted.