MACROMEDIA FLASH 8-GETTING STARTED WITH FLASH Getting Started page 116

116 Tutorial: Building Your First Flash Application
13. Still in the Align panel, click the Align Horizontal Center button.
Clicking the Align Horizontal Center button
The rectangle is now precisely centered on the Stage.
The black rectangle centered on the Stage
14. Click outside the Stage to deselect the black rectangle.
15. In the Tools panel, select the Rectangle tool.