Equation 1–297 becomes a diffusion-only transport equation with a uniform source term of unity:

(1–304)

Dirichlet conditions of are applied on boundaries of interest (such as walls), and Neumann (or zero flux) conditions are applied on other boundaries. Equation 1–303 is then evaluated, replacing with ( is always positive) and is interpreted as the distance to the nearest boundary where was set. This gives the following expression for desired distance:

(1–305)

Because is always positive, the wall distance is also always positive.