Normal TagBasic Tag
Many NURBS modelers export relatively poor-quality meshes which can be recognized by the errors in shading. Several modelers let you optionally embed "Vertex Normals" (these are Normals that exist for each point; depending on the surface, this can amount to several Normals per point). This serves exclusively to display and render the object correctly.
Normal tags can react very sensitively to being edited at point level or when Deformers are used. This shading can then produce artefacts.
Normals can be displayed numerically (