Thereby, GEO provides an unambiguous measure for the quality of approximate geometries (the higher the GEO value, the worse the geometry). As such, it circumvents a need for comparing errors in possibly dozens of bond lengths and angles to rank approximations. These features make GEO an ideal quantity for assess-ing the quality of geometries of any molecule and any method so long as the reference geometries are available. Furthermore, GEO can also tell us what fraction of the total error is due to geometry, and what due to total energy. In Appendix A, we show the decomposition of the total error of an electronic structure calculation into geometric and non-geometric part. This decomposition has shown that geometric errors are typically small (but not negligible) part of errors for e.g., atomization energies, but can account for most of the error for weak interactions. It also enabled identification of specific situations where better results are obtained by using less accurate structures due to error cancellations between the geometric and nongeometric part of the total error. Computing GEO by Eq. 1 requires access to the exact geometries and exact energies at approximate geometries. For single-reference systems, CCSD(T) with large enough basis set provide accuracy that rivals experimental geometries, 10 so we can consider them 'exact'. VB used CCSD(T)/aug'-cc-pV5Z 11,12 as a reference to calculate GEO for a set of small molecules that had been earlier optimized by Karton and co-workers. 11 For somewhat larger systems (e.g., aromatics containing two benzene rings), running CCSD(T) geometry optimizations with a large basis set becomes too expensive. For this reason, VB had to rely on B2PLYP as a proxy reference, given its nearly CCSD(T) performance for small molecular structures. In a more recent work, Bakowies and von Lilienfeld extended this analysis to a larger set of small molecules, and even built empirical corrections for the part of atomization energies error that is due to approximate geometries. Here an important question arises: When accurate reference geometries are available, can the use of expensive single point calculations at approximate geometries needed to calculate GEO by Eq. 1 be by-passed? Such calculations make the benchmarking of geometries more expensive, and thus pose the restrictions regarding the molecular size. The answer to this question is yes, as assessing geometric performance of approximations by calculating GEO values can be greatly simplified by introducing its approximation: