The difference between the two can be substantial (tens of Hz), while it is still larger than zero for most 1 H resonances -a fact that cannot be overemphasized. Importantly, this difference is not an uncertainty of the NMR measurement, but a natural property that is predicated on the QM foundation of NMR spectroscopy. As such, even if the differences are in the order of a few Hz and might be considered as small, they are highly significant and can be determined with mHz accuracy.