This part of the standard specifies the principles of transmission techniques. Transmission techniques can be used for: - detection of imperfections; - determination of attenuation. The general principles required for the use of ultrasonic examination of industrial products are described in part 1 of this standard. The transmission technique is used for examination of flat products, e.g. plates and sheets. Further, it is used for examinations e.g.: - where the shape, dimensions or orientation of possible imperfections are unfavourable for direct reflection; - in materials with high attenuation; - in thin products.