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So I get the difference between global space (or world space, whatever you want to call it) and local space-- global space looks at locations in a 3D Cartesian Graph that has a fixed orientation/location which is independent of the objects within it while local space bases its 3D graph's orientation/location off of the object that that particular space belongs to. Then normal space is dragged into the mix and it gets confusing: I've tried to spot a difference between local and normal space by using the transformation orientation and, as best I can tell, normal space and local space operate with the same orientation/location.

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  • $\begingroup$ Related blender.stackexchange.com/questions/59107/… The normal transform orientation is explained in the tool tip. Test in edit mode, default cube, face select. With all faces selected the normals will sum to zero. Not sure what the fallback is in this case. In blender global space could be called "scene" space. (or local space of scene object) This is still somewhat arbitrary. If we model Earth in one scene and Mars in another we would most likely use planet origin as scene origin. $\endgroup$ – batFINGER Apr 16 at 5:58
  • $\begingroup$ @batFINGER This raises a question for me, too. Considering only triangles for a moment, Normal Z would be the cross-product of any two edges.. but how does Blender choose which vector to cross with Normal Z to fix Normal X (and subsequently, Normal Y?).. I can't find any correlation with vertex index, or loop index... $\endgroup$ – Robin Betts Apr 16 at 10:26
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    $\begingroup$ @RobinBetts for aligning object to anothers face normal orientation. blender.stackexchange.com/a/94047/15543 $\endgroup$ – batFINGER Apr 16 at 10:47
  • $\begingroup$ ahhh.. the calc_tangent_edge methods look as if they might be clues.. thanks. it's time I committed myself to rifling through Blender's code.. learning to navigate it would be a big challenge, though... $\endgroup$ – Robin Betts Apr 16 at 11:46
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Probably your confusion derives by using a cube as example, which is an ultra regular object. Try Suzanne instead: the difference between local and normal is evident. The normal is calculated by the average of all normals of selected faces.

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  • $\begingroup$ It's funny because I actually did use a different object after the cube, I used a cone that I set up with 3 vertices (in the settings, physically the object has 4 verts including the top one) so that I got a tall tetrahedron (I don't know the term for it, isosceles tetrahedron?). I guess the default settings for a cone on a tetrahedron result in an ultra regular object as well. $\endgroup$ – thepufferfish Apr 16 at 23:47

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