A zoom in to part of the current view is very
simply done by left-clicking one of the corners of the area you want
to enlarge and, while holding the button down, sliding the mouse to the opposite
corner of this area. Just releasing the mouse button then instigates the calculation
and display of a new view of the defined area.
A zoom out of the current view can also be simply
accomplished by pressing the " Ctrl " key then
left-clicking one of the corners of the area you want to specify. Then,
while holding the button down and continuing to press the “Ctrl” key, just
slide the mouse to the opposite corner of this area. Just releasing the mouse
button then instigates the calculation and display of a new view. The former
view will then take the place of the area defined by the mouse.