A center clamp used with a machining tool having an annular edge has a C-shaped body having an inner end inside the edge and an outer end outside the edge and spaced from it along a clamp axis. The charging member charges a surface of an image carrier and includes a charging member body and axial-end members. The emissive material emits light having a second optical characteristic when illuminated with light having the first optical characteristic. A bracket, with openings for fasteners for attaching the assembly to wall members, can be made a part of the frame. For example, the techniques may be used for measuring thicknesses, optical properties, composition, porosity and roughness of a film or stack of films. An endless belt is sequentially routed over the tail pulley, the first nose bar, the drive pulley, the second nose bar, and the snub pulley.