**Figure 8**
Rotation-function likelihood. (*a*) The unit cell contains six symmetry-related molecules. For a given orientation of the search, the orientation but not the position of the six molecules is defined. Therefore, the amplitudes but not the phases of the six corresponding structure-factor contributions are defined. The atoms in the molecules have errors in their positions and scattering, indicated by the arrows and concentric circles, respectively. The molecule in the orientation giving the largest scattering is shown in magenta. (*b*) The largest model structure-factor contribution, *F*_{big}, is given a phase α relative to the observed structure factor* F*_{o}, with the other model structure-factor contributions making a `random walk' around the end of this one phased structure-factor contribution. (*c*) The resulting probability distribution for **F**_{o} is a two-dimensional Gaussian centred on *D***F**_{big}, shown with grey shading. |