Hi hallsadvancedformula, if I'm understanding right you're adding a bisector line so that you can drag both the line and the circle to a new location, dragging from the midpoint of the line (same as the center point of the circle) as the base point?

If that's the case then the main simpler way to do it is like Martin writes above - use the Transform > Move command instead of direct object dragging. The Transform > Move command will allow you to do 2 individual point picks for the base point and the target point, and you can snap the base point onto the center point of the circle. That should then do what you need without needing to draw any additional separate line segment.

Dragging works as a kind of quick shortcut for moving objects around, but since dragging is initiated by dragging from a spot that's on the actual curve itself that won't work for dragging a circle by its center point. But the Transform > Move command allows you to pick any point that you need as the base point, it doesn't have to be one directly on the curve like dragging uses.

In the future I think I'd like to experiment with making a draggable center point that would then enable you to do what you were originally thinking about. I'm a little worried about filling up the working area with special handles though, it can kind of make a sort of screen clutter which I've tried pretty hard to avoid in general. That's one reason why I haven't really jumped into doing that quite yet.

But in the meantime before that is available the Transform > Move command should allow you to do what you need more easily without needing to create any bisector lines.

Hope this helps!

- Michael