Nuclei far off stability in theNpNnscheme

The phenomenological prediction of properties of nuclei far off stability is greatly simplified in the $N_{\mathrm{p}{N}_{\mathrm{n}}}$ scheme for three reasons: the systematics for each observable is smooth, the similarity of different regions provides a paradigm for unknown cases and, primarily, the $N_{\mathrm{p}{N}_{\mathrm{n}}}$ scheme often transforms the process of extrapolation into one of interpolation. The same ideas find expression in the concept of $N_{\mathrm{p}{N}_{\mathrm{n}}}$ multiplets that can link known and unknown nuclei.