Retention distance
Retention distance, or "R", is a concept in thin layer chromatography, designed for quantitative measurement of "equal-spreading" of the spots on the chromatographic plate and one of the Chromatographic response functions. It is calculated from the following formula: formula_1 where "n" is the number of compounds separated, "R" are the Retention factor of the compounds sorted in non-descending order, "R" = 0 and "R" = 1. Theoretical considerations. The coefficient lies always in range <0,1> and 0 indicates worst case of separation (all R values equal to 0 or 1), value 1 indicates ideal  equal-spreading of the spots, for example (0.25,0.5,0.75) for three solutes, or (0.2,0.4,0.6,0.8) for four solutes. This coefficient was proposed as an alternative to earlier approaches, such as delta-Rf, delta-Rf product or MRF (Multispot Response Function). Besides its stable range, the advantage is a stable distribution as a random variable, regardless of compounds investigated. In contrast to the similar concept called Retention uniformity, "R" is sensitive to "R" values close to 0 or 1, or close to themselves. If two values are not separated, it is equal to 0. For example, the "R" values (0,0.2,0.2,0.3) (two compounds not  separated at 0.2 and one at the start ) result in "R" equal to 0, but "R" equal to 0.3609. When some distance from 0 and spots occurs, the value is larger, for example "R" values (0.1,0.2,0.25,0.3) give "R" = 0.4835, "R" = 0.4066.