You can select the position and size of an area to zoom in on with Zoom To Rectangle 
.
To Select Zoom To Rectangle
-
Click the Zoom To Rectangle
button on the toolbar.
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Choose View > Zoom > Zoom To Rectangle.
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Press ⌘*
Magnify an Area with Zoom To Rectangle
-
Select Zoom To Rectangle
.
The pointer changes to the Zoom To Rectangle pointer
.
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Drag a rectangle around the area you want to zoom in to.
-
Release the mouse button to zoom in.
Zoom To Rectangle is automatically deselected after you have used it.
