# 3. Continuity Reconfiguration in a region of $u$ is a fact of $u$ itself. It is not private to one part of the extent. The surrounding extent must accord with that change. If it did not, the reconfiguration could not be said to have occurred in $u$ at all. That makes an ordering of registrations possible. Label two such ordered registrations $1$ and $2$. Then $u_2$ is related to $u_1$ through a flow field $\mathbf{S}(\mathbf{r};1,2)$, which encodes how one registered distribution changes into another. The difference $$ u_2(\mathbf{r})-u_1(\mathbf{r}) $$ is understood as the result of a continuous redistribution of energy within itself, described by a flow connecting the two registrations. Energy in a region changes only by crossing its boundary to a neighboring region. In one direction, say the x-direction, the statement is $$ u_2-u_1+\partial_x S_{12}=0. $$ Here $S_{12}$ refers to the redistribution flow connecting registrations $1$ and $2$. This is accounting of energy, not yet its dynamics. It is like accounting for the brightness of the pixels on a screen without yet recognizing the image they compose.[^platos-allegory] Continuity is therefore the minimal consistency requirement for transport. It gives closed bookkeeping. We now turn to exploring the implied consequences of this energy accounting in free space. [^platos-allegory]: As Plato and many others observed, one can become skilled at recognizing images, patterns, and regular sequences of appearance while remaining ignorant of what produces them. Physics can encode repeatable regularities without thereby laying hold of the underlying causes. Even so, such encoding is far better than treating the screen as uniform brightness alone.