which is the mass of water inside the cv that entered at \(t_{in}\) (independently of when they will go out. This \(s\left(t,t_{in}\right)\) is what She measures in her table. There is an apparent the conundrum that while integration in (2) is on all future times, \(s\left(t,t_{in}\right)\)it is known at time \(t\ \): but this is due simply to mass conservation of which the future must be respectful. By definition: