This expresses the number of peaks which can be resolved in a given part of the chromatogram between the peaks of two consecutive n-alkanes with $z$ and ($z+1$) carbon atoms in their molecules: $$\text{SN}=\frac{t_{\text{R}(z+1)}-t_{\text{R}z}}{w_{\text{h}z}+w_{\text{h}(z+1)}}-1$$ In the German literature the symbol $\text{TZ}$ (trennzahl) is commonly used to express the separation number. As the separation number depends on the n-alkanes used for the calculation, they always must be specified with any given $\text{SN}$ value.