Adobe Extending Flash Professional CS5 - Manual (Page 193)

171 EXTENDING FLASH PROFESSIONAL
Document object
Last updated 5/2/2011
Description
Property; specifies the zoom percent of the Stage at authoring time. A value of 1 equals 100 percent zoom, 8 equals 800
percent, .5 equals 50 percent, and so on.
Example
The following example sets the zoom factor of the Stage to 200 percent.
fl.getDocumentDOM().zoomFactor = 2;