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From SofTutor for AutoCAD 3D - 3D Mirror Command
Topics covered in this video are:
Mirroring An Object By Providing 3 Points
Mirroring An Object On The Same Plane
Mirroring An Object On The ZX Plane
Mirroring An Object On The YZ Plane
Mirroring An Object On The XY Plane
XYZ UCS Modify
3D XYZ Axis UCS