What's the purpose of the "-1"?
It's a traditional method of making a mirror copy, but it has pitfalls. One problem is that when applied to a 3D object, the result is NOT a mirror copy (i.e., with chirality opposite the original), but simply a rotated copy. The attached .jpg illustrates the difference between mirror copying and negative scaling.
Another quirk is that using a negative value of not exactly 1 often produces a negative object
which responds weirdly to Boolean ops and thus can damage your drawing. To see one aspect of this behavior, open the attached NegativeObject.tcw and try 3D-slicing the object. (It was created in v10.5 and should open OK in that version or any later version.) After slicing, zoom way out to see what really happened.
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