(a) A photograph of the sample fixed to the holder. (b) Sample and X-ray beam geometries. L is the distance from the fixed end to the free end, l the distance from the free end to the incident plane of the X-rays and D the displacement of the crystal end from the flat surface. (c) A schematic diagram of the measuring system. xL is the distance between the incident point of the X-rays and the crystal edge in the incident plane.