This AutoCAD routine from Kent Cooper mirrors a selection set both ways — about a user-specified point at the intersection of two perpendicular axes, and at a user-specified axis angle — in one step. It remembers your base point and angle and offers them as defaults for subsequent uses, so added elements can be mirrored both ways in the same circumstance without re-selecting the base point and angle. After you load the LISP file, type in the command MBW. Select the objects first, followed by a base point and angle. As always, Kent’s LISP code contains plenty of notes and comments.