Zooming into/out of Diagrams
To zoom into or out of a diagram, do one of the following:
•Run the menu command View | Zoom In (Ctrl+Shift+I) or View | Zoom out (Ctrl+Shift+O).
•Select a predefined percentage value from the Zoom toolbar.
•Hold down the Ctrl key while rotating the mouse wheel.
To fit the diagram area to the visible window:
•Run the menu command View | Fit to window (or click the Fit to window 
toolbar button).