Let $({\mathfrak{V}},{\mathfrak{L}})$ be a formal ${K^{\circ}}$-model of $(V,L)$ as in 2.2. Then we get an associated formal metric ${\|\hskip 4.30554pt\|}_{\mathfrak{L}}$ on $L$ uniquely determined by requiring $\|s\|_{\mathfrak{L}}=1$ on the generic fibre $W$ of any frame $s$ of ${\mathfrak{L}}$ over any formal open subset ${\mathfrak{W}}$ of ${\mathfrak{V}}$. This is well-defined because a change of frame involves an invertible function $f$ on ${\mathfrak{W}}$ and we have $|f|=1$ on $W$.