Correlation lengths can vary locally and are subject to some interpretation (Section 3.2.2); however, it's clear that without knowing more, the property prediction of the GB of interest might be OK, or it might be completely off. The BRK model (which uses 388 GBs) works around this lim-itation by imposing prior information: a "scaffolding" of GBs at high-symmetry cusps is used, and it is assumed that the function varies monotonically from point to point everywhere else. For a wellstudied property (GBE) and a well-studied material system (FCC), this domain knowledge can be successfully baked in. But what if the property or material system is not so well understood? These are cases where the VFZ framework is especially useful.