Geometrical features of micro-systems can be determined by either tactile or optical profiling techniques, which show different non-linear transfer characteristics. This has to be considered especially, if the instruments operate close to their physical limitations. Depending on the specific measuring task either point-wise or areal optical measurement may be advantageous. Hence, examples for both approaches are discussed. Furthermore, systematic effects, which are related to the measuring principle have to be taken into account, e.g. if sharp edges or slopes are present on the measuring object. As it is shown, for white-light interferometry these difficulties can be solved by a two-wavelength technique. This has to be considered especially, if the instruments operate close to their physical limitations. Both on the specific measuring task either pointed, are-wise or areal optical measurement may be advantaged. furthermore, systematic for both approaches are discussed. Furthermore, systematic effects, which are related to the measuring principle have to be taken into account, eg if sharp edges or slopes are present on the measuring object. As it is shown, for white-light interferometry these difficulties can be solved by a two-wavelength technique.