A rocking curve of the analyser lamella with path 1 of the interferometer blocked, cf. Fig. 3. The error bars lie within the bullets. The theoretical prediction (solid line) is calculated by convolving the product of three Bragg reflections (the triple-bounce Bragg monochromator) and two Laue reflections (the splitter and mirror lamella) with the final Laue reflection by the analyser. The overall agreement is very good. We attribute the remaining discrepancies to imperfections of the crystal geometries on the level of a few micrometres.