“…Equation (1) can be used (1) in the case of the lines originating from the same type of transition (e.g., resonances or off-resonances; Purić et al 1985), and in transition arrays within one stage of ionization (Z c ¼ const), or within several stages of ionization (Z c 6 ¼ const; Purić et al 1991Purić et al , 1993Purić & Šćepanović 1999;Šćepanović & Purić 2003); (2) within particular isoelectronic sequences (see, e.g., Purić et al 1988); and (3) within a given isonuclear sequence (see, e.g., Purić et al 1988). …”