relative retention, \(r\)

in column chromatography
https://doi.org/10.1351/goldbook.R05277
The ratio of the adjusted or net retention volume (time) or retention factor of a component relative to that of a standard, obtained under identical conditions: \[r=\frac{V_{\text{R}i}^{'}}{V_{\text{R}\left(\text{st}\right)}^{'}}=\frac{V_{\text{N}i}}{V_{\text{N}\left(\text{st}\right)}}=\frac{t_{\text{R}i}^{'}}{t_{\text{R}\left(\text{st}\right)}^{'}}=\frac{k_{i}}{k_{\text{st}}}\] Depending on the relative position of the peak corresponding to the standard compound in the chromatogram, the value of r may be smaller, larger or identical to unity.
Sources:
Orange Book, 2nd ed., p. 105 (http://media.iupac.org/publications/analytical_compendium/)
PAC, 1993, 65, 819. 'Nomenclature for chromatography (IUPAC Recommendations 1993)' on page 843 (https://doi.org/10.1351/pac199365040819)