I dont fully understand about Recalculate normals I dont really get this functions without explanations or images,
&quot;These tools will recalculate the normals of selected faces so that they point outside (respectively inside) the volume that the face belongs to. The volume does not need to be closed; inside and outside are determined by the angles with adjacent faces.&quot;
what does the volume means? and I dont get respectively inside which mentioned above.
somebody please explain the upper italic section please.
The normal of a face is the blue line, starting from the center of the face and pointing as much orthogonal as possible away from a face: it can point in two directions: one side of the face or the other.
Two connected faces, if they stay onto two different planes, can be considered as part of a &quot;sphere&quot;. Normals are calculated  outside or inside the volume of that ipothetical sphere.
In the case of more than two faces the calculation is repeated, guessing wich is the part to be considered &quot;inside&quot; and which one &quot;outside&quot;, even when the &quot;Volume&quot; is not closed (as with the two faces example).