Offsets a single polygon face (aka polyline segment) to a partition centerline or to match an existing line segment. Select a face by first selecting a single polygon, then clicking on the circle designating the midpoint of the face. The circle will display as filled to indicate selection. Then enter CTRL-F (or select OffsetFace from Modify menu). Then, as prompted, click on the line segment representing the opposite side of the wall. A normal click will offset the face to the midpoint and a shift-click will offset the face to match the selected segment.