residue contact strengths (1) are distance based, not energy based; (2) rep- resent a coarse-grain approximation of actual interaction energies; (3) have improved signal-to-noise ratios through analysis of mul- tiple ligands and crystallographic conformational ensembles; and (4) provide a reasonable compromise between a binary definition of interatomic contact based on a cut-off interatomic distance and the complexities and ambiguities of accurate energy calculations for conformationally variable crystallographic ensembles.