The Object Preview window displays the current 3D model. Also displayed is the clipping plane, showing how the object relates to an imaginary plane at the point where the Z axis (front – back) = 0.
Click and drag to change the orientation of the tool; drag the tiny crosshairs to change the object’s center. Hold the SHIFT key while dragging to snap its orientation to the nearest 45-degree angle. To hide or show the clipping plane, click the ‘+’ button in the upper-right corner. To freely spin the object preview, click the arrow button, and change the speed of spinning by clicking and dragging in the window.