band 10 frequency the actual band 10 velocity is calculated from the band 10 frequency and the link thickness of the band 10 or the link length of the chain the actual band 10 slip now results from the comparison between the actual band 10 velocity and a theoretical band 10 velocity calculated from the measured rotational speed ratio n primary n_secondary and the variator 12 geometry in a variant of the vibration evaluation it can be provided that the actual band 10 slip be determined by a comparison between a theoretical and an actual variator 12 ratio therefore the actual variator 12 ratio resulting from the measured rotational speeds of the variator 12 is compared with the theoretical variator 12 ratio appearing as a result of the band 10 velocity and the running radius since geometric and tribologic slips overlap an adequate differentiation is provided according to the invention the knowledge of an existing variator 12 adjustment results for ex from the iv regulator contact of the ratio regulation of the electronic transmission control 26 or from the requirement according to driving strategy in the existing operating point the vibration measurement is accordingly estimated during the evaluation according to the invention typical vibration features are identified in the vibration signal 16 sm 16 am which result from tribologic slip in the band pulley contact the frequency analysis delivers typical frequencies conditioned by tribologic slip analyses in the time domain deliver typical tribologically determined patterns in the time signal according to the invention adequate reference values for estimating the measured values are stored in the electronic transmission control egs 26 within the scope of one variant.