Atomic-number similarity of the $K$ and $L$ X-ray terms in multielectron atoms

Dependences of experimental $K$, $L_I$, $L_{II}$, and $L_{III}$ X-ray levels on the atomic number different from Moseley's law have been revealed. The simplest cubic polynomial approximations of the found dependences make it possible not only to describe experimental data with an accuracy better than one percent but also to control their reliability.