Clean geometry is a requirement for CheckMate Pro Certification

After you finish your model, you’ll need to take a few moments to verify that the geometry is clean. Clean geometry means:

• No coplanar/coincident faces. This means faces that occupy the same space, which will cause flickering during animation. It is fine to have intersecting faces that cut through one another.
• No overlapping/coincident vertices (vertices that should be welded but aren’t)
• No isolated vertices
• Normals facing out

While your modeling practices probably prevent these problems most of the time, checking your models is easy and takes just a few minutes.