Click the icon and then click on any control point in one of the orthogonal projection views. The row of control points corresponding to the clicked point will be highlighted in red. Drag the mouse across the screen and release it when you reach the desired position.

Other rows of control points can be added incrementally to the drag operation. Individual control points can be removed from the drag operation by clicking with the CTRL key pressed.

The information box (above the 3D view) displays information about the drag distance.

Switch between orthogonal projection views and continue dragging.