Notes

¹Supplementary material has been deposited in the IUCr electronic archives (Reference: HX5036 ). Services for accessing this material are described at the back of the journal.

²Note that in IRF equations the FWHMs _i, _i always replace the corresponding distribution function widths '_i, '_i that appear in the probability expressions.

³We observe that flattening the collimating mirror translates into a fairly poor energy resolution (beam of divergence _m directly impinging on the first monochromator crystal). Therefore, the flat-flat optical configuration is not recommended for high-resolution powder diffraction studies, unless the intrinsic divergence of the source is very small as in the case of undulators (Gozzo et al., 2004).