The coefficient lies always in range <0,1> and 0 indicates worst case of separation (all Rf 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, Rd is sensitive to Rf values close to 0 or 1, or close to themselves. If two values are not separated, it is equal to 0. For example, the Rf values (0,0.2,0.2,0.3) (two compounds not separated at 0.2 and one at the start ) result in RD equal to 0, but RU equal to 0.3609. When some distance from 0 and spots occurs, the value is larger, for example Rf values (0.1,0.2,0.25,0.3) give RD = 0.4835, RU = 0.4066.
![{\displaystyle R_{D}={\Bigg [}(n+1)^{(n+1)}\prod _{i=0}^{n}{(R_{F(i+1)}-R_{Fi}){\Bigg ]}^{\frac {1}{n}}}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/79241f2396f82154973ed818c400fbe43dce38b0)
