The requirements on the surface quality of rolled sheet metal are continually increasing. This may be steel sheet which is used, for example, for stainless steel fronts in kitchens, or also aluminium sheet used in the automotive field. The surface must be flawless to offer the customer a high quality visual appearance. Consequently, measurement equipment is employed in rolling mills to acquire the so-called flatness of the rolled sheet metal. Flatness is taken to mean the surface evenness of the sheet in the unstressed state.