Поскольку электронные оболочки химических элементов имеют симметрии в координатах (n,l) и (n+l, n-l) одновременно, изображение их совокупности требует как минимум трех измерений

“could be considered complete in its fundamental structure, as the periodic variations of configuration energy align perfectly with the known physical and chemical properties of the elements”. “Allen's approach is often viewed as a major step in the transition from empirical arrangements of elements to a system driven by fundamental physics”.