Menu: Mesh->Draw->Boundary layer
With this option you can see the first layer height of the boundary layers set in the model (see Boundary layer). In '2 dimensional' option the lines from wich the boundary layer will grow are shown, and in '3 dimensional' the surfaces.
In cases where two boundary layer meshes grow from the same geometrical entity (one for each side), the minimum value of the first layer heigt is shown.