Control B
Click - drag:
If Control A is selected as anchored, the tool will pivot around the point at Control A.
If Control C is selected as anchored, the tool will pivot around the point at Control C.
If Control B is selected as anchored, the whole tool will move freely around the screen.
Left Click:
Selects Control B to be anchored. XgoldenSection can be dragged anywhere on the screen by dragging the middle control.
The anchor point can also be selected in preferences panel.