Probability distribution for maximum likelihood in the presence of unbuilt structure. This figure shows the probability distribution in the complex plane for the case where, in addition to the modeled parts of the crystal, there is a component present in the crystal for which an explicit model has not been built. This distribution is an elaboration of that shown in Fig. 2(b). That distribution is convoluted with the probability distribution of the structure factor calculated from the envelope where the additional atoms are believed to lie and weighted by the number of atoms in this substructure (which can be represented as a distribution centered on the vector Fpart). The resulting distribution has a center that is offset by Fpart and a width that is inflated relative to that of Fig. 2(b) by the additional uncertainty inherent to the unbuilt model.