Where:
N = number of rate cells in the class.
i = denotes a rate cell (i = 1, 2, . . ., N).
Ri,n = planned rate of rate cell i.
Ri,c = current rate of rate cell i (for rate adjustment involving a rate increase) or rate from most recent rate adjustment involving a rate increase for rate cell i (for a rate adjustment only involving a rate decrease).
Vi = volume of rate cell i.
39 C.F.R. §3030.128