Table \ref{table:vsexp} shows the comparison of QM, ProCS15 and several common chemical shift predictors to experimental values. The first two rows use the OPBE/6-31G(d,p) and ProCS15 chemical shielding predictions used to construct Table \ref{table:vsqm} and therefore use the PM6-D3H+ optimized structures of Ubiquitin and GB3. However, most future use of ProCS15 will be based on structures optimized with force fields so prediction of the remaining rows is done using structures optimized with the CHARMM22/CMAP force field. The ProCS15 predictions based on the CHARMM22/CMAP-optimized structures include the \(\Delta \sigma_{w}\) term (cf. Eq \ref{eqn:procs}). The \(a\) and \(b\) factors in Eq \ref{eqn:scaling} are found by linear regression to the experimental values for each atom type. In order to offer a fair comparison RMSD values are computed after a linear fit to the experiment for all methods.