Samsung Galaxy S III User Manual page 31

Rotate
For most screens, you can automatically change the screen orientation from portrait to
landscape by turning the phone sideways. When entering text, you can turn the phone sideways
to bring up a bigger keyboard.
Note: The Auto-rotate check box needs to be selected for the screen orientation to
automatically change. To make this selection, press
Display > Auto-rotate screen. See
Phone Basics
Auto-rotate screen for more information.
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> > Settings and tap