The nucleus-independent chemical shift (NICS) is a computational method that calculates the absolute magnetic shielding at the center of a ring. The values are reported with a reversed sign to make them compatible with the chemical shift conventions of NMR spectroscopy. In this method, negative NICS values indicate aromaticity, and positive values indicate antiaromaticity.  There are a variety of methods to calculate NICS values, however, the most robust method for calculating NICS values involves scanning the molecule in a NICSzz scan. In this process, the NICS value is calculated above the rings, and this allows for evaluating the aromatics of each ring, which is especially useful for polycyclic compounds.