14 as viewed over the length l see fig2 b according to fig4 and 5 three flat bars 14 u2032 14 u2033 14 u2032 u2033 have clothing 19 u2032 19 u2033 19 u2033 u2032 respectively flat bar 14 u2033 glides with surfaces 14 of the slide pins 14 1 through 14 4 in the direction e over the stationary support 29 a the measuring surface 24 u2032 of the stationary sensor 24 faces at a distance d the points of the clothing 19 u2033 of the flat bar 14 u2033 the light section sensor 24 generates in the direction of the flat bar length see fig5 a laser beam 25 which impinges on the slide surfaces 14 of the slide pins 14 1 through 14 4 as well as on the flat bar clothing 19 u2033 as the flat bars 14 pass under the sensor 24 the height profile shown in fig5 is obtained for an evaluation the measured value of the two slide pins 14 3 14 4 is deducted from the maximum value which is to be filtered out via the constant pin distance the height difference c thus obtained is utilized for checking the flat bars 14 uniformity.