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. However, as soon as you edit such an object at point level the Normals tag will no longer match the object and completely incorrect shading will result. You can, however, move, rotate and scale the object with no problems.
As soon as the Normal tag is deleted the normal shading mode will be used.
Normals can be displayed numerically (