Vector fields
A mesh layer with a vector field (for example a SimNIBS E field, three components per node or element) can draw it as glyphs — arrows at each mesh vertex/element centroid or at each tetrahedron's centroid, scaled by fixed, linear, sqrt, or log length scaling. The legend line under the colour bar states the scaling as a full sentence, so the arrows' lengths mean something specific rather than an unlabelled scale. A scalar field (no direction) never appears in the glyph selector — only fields with more than one component can drive an arrow.
