Let us assume that $K$ is algebraically closed. Let $\varphi$ be a model function determined by a vertical Cartier divisor $D$ on the algebraic ${K^{\circ}}$-model ${\mathscr{X}}$ of $X$. We assume that the special fibre ${\mathscr{X}}_{s}$ is reduced. Then $\varphi\geq 0$ if and only if the Cartier divisor $D$ is effective.