The retention factor (R) may be defined as the ratio of the distance travelled by the solute to the distance travelled by the solvent. It is used in chromatography to quantify the amount of retardation of a sample in a stationary phase relative to a mobile phase. R values are usually expressed as a fraction of two decimal places. 
* If R value of a solution is zero, the solute remains in the stationary phase and thus it is immobile. 
* If R value = 1 then the solute has no affinity for the stationary phase and travels with the solvent front. 
For example, if a compound travels 9.9 cm and the solvent front travels 12.7 cm, the R value = (9.9/12.7) = 0.779 or 0.78. R value depends on temperature and the solvent used in experiment, so several solvents offer several R values for the same mixture of compound. A solvent in chromatography is the liquid the paper is placed in, and the solute is the ink which is being separated.