ZOOM takes an image that is already being displayed and displays
the zoomed region in a new window. The user uses the cursor and clicks
with the left button to chose the center of the region to zoom (the
selected region is displayed each time the left button is clicked). The
middle button allows the zoom factor to be selected using a menu. The
right button exits the zoom option (the zoom window is deleted upon
exiting ZOOM). An example would be:
IDL> tvscl, data(*,*,5)
IDL> zoom