Zoom Tool 

     The Zoom Tool is used to move in and out of a particular part of the page.
 Drag out a rectangle over the area you want to enlarge and release. The page 
 view is scaled so that region now occupies the largest area possible in 
 the current window.
   To zoom out, hold down the Option  key and click. All sequential clicks with 
 the Zoom tool change the view scale as specified in Preferences 
 (originally set to 25%).  This value is displayed in the Object Width 
 box on the Attribute Toolbar. You can easily change it (see the 
 Object Width box help section). The current amount of a document
 view scale is displayed in the Object Height  box (see the Object 
 Height box help section). You can change it by simply editing  
 the value in the box.
     The Zoom tool stays selected until you change to another tool.