carrier element 21 as viewed from the transmission unit 11 transmission patterns tm are formed in the calculation unit 13 of which transmission patterns one is shown symbolically in fig2 reflection patterns rm are formed in the calculation unit 13 on the basis of the test radiation 8 r received along the reflection axis rx of which reflection patterns one is likewise shown symbolically in fig2 the transmission pattern tm shows the silhouette of or the shadow cast by the carrier element 21 depending on the wavelength of the electromagnetic test radiation the silhouette of the sheath 215 in the case of wavelengths in the nm range or the silhouette of the metallic wire ropes 21 a 21 b in the case of wavelengths in the u03bcm range is measured the reflection pattern rm formed on the basis of reflected electromagnetic test radiation shows the structure of the surface of the metallic wire ropes 21 a 21 b in a detailed illustration and typically has a greater information content than the transmission pattern tm fig2 shows that a peripherally arranged wire 211 of one of the wire ropes 21 a has broken open and the wire ends thereof protrude outward or are frayed out as a result of this damage there is an influence on both the transmission pattern tm and the reflection pattern rm as indicated in fig2 the laterally protruding wire ends 211 interrupt the test radiation at the relevant point and reflect a corresponding radiation portion back via the reflection axis rx thus radiation portions are missing in the relevant region for the formation of the transmission pattern tm while there.