CENTERLINE command
Creates a centerline.
                Icon: 
Alias: CL
Description
Creates a centerline geometry associated with two selected lines or polyline segments.
Note: Centerlines are drawing reference entities to indicate
                    axes of symmetry.
            Method
When applying a centerline to the intersection of two lines, the location of the picked points determines the direction of the centerline.
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The lines and polyline segments can be selected inside blocks and in drawing view viewports. You can pick two segments of the same polyline.
Note: The centerline is associative, so when one or both lines
                    are moved, the centerline repositions itself.
            Note: Centerlines can be edited through grips. It can be moved
                    and lengthened by dragging the grips. The CENTERRESET command can be used to
                    reset the centerline.