The sample is mounted to a Huber goniometer for which three linear stages for x, y, and z translation are used to place the sample in the center of rotation. The sample-todetector distance is 400 mm. The lateral dimensions of the primary beam (1 9 5 mm 2 ) are defined by two slits in the horizontal and the vertical direction (S1). A vertical slit behind the sample (S2) screens scattering that does not stem from the sample; additional slits in front of the detector (S3) define the resolution of the instrument. All scans are performed at slit widths of 2 mm (S2) and 0.5 mm (S3). For the given sample-detector distance, the latter yields a resolution of 0.07°or 0.01 Å -1 . With these settings, the profile of the primary beam typically has a full width at half maximum (FWHM) of 0.2°. The diffractometer motor and the detector controls as well as the monitor counter readout are accomplished by the SPEC software (Certified Scientific Software, Cambridge, MA, USA).