He and She annotate their action in two tables whose rows are marked by the current clock time and whose columns are the injection times, \(t_{in}\) the times when rain have fallen. Clock time is continuous but sampled at discrete time steps while \(t_{in}\) is discrete cause the nature of precipitation. The matter can be presented in a quite abstract manner, but here we rely on a simple example.
Therefore, assuming that we had three precipitations at time \(t_{in}=\ \left\{0,3,5\right\}\) of mass (or volumes or moles, the units specification is unnecessary at moment) \(P=\left\{20,18,15\right\}\)respectively , She and He can organise their record according to the following tables which grow one row any time step and which we show here in their definitive form, after all precipitations we are interested about exited the cv:
For She, it is: