Windows Phone Update 3 finally adds a feature that users of other mobile devices have long enjoyed: Screen rotation lock. This toggle enables you to "lock" the screen orientation in either portrait or landscape mode so that inadvertent shifts in the position of the device don't trigger screen redraws.
The need for a screen rotation lock is obvious to anyone who has tried to read in bed or perform some similar action where shifts in the position of the phone trigger its screen rotation functionality. It can be annoying, and made doubly annoying when you need to re-shift the device purposefully to get the display back to the orientation you prefer.
Of course, rival platforms such as Android and iOS build this functionality into a slide-in control panel-type UI that is accessible via anywhere in the system via an edge swipe (from the top right in Android or the bottom in iOS). And though Microsoft perhaps should have built this toggle into the overlay that appears when you tap a volume button, it did not. So the feature is a bit inconvenient to access. (Perhaps it will appear in a future notification center UI.)
There is one other caveat, which should be obvious, though I'll mention it for completeness: Because some Windows Phone experiences are hard-coded to a certain screen orientation—the Start screen is always displayed in portrait, for example, while many games only appear in landscape—locking screen rotation will not affect these apps, games, and other screens. It can only affect those experiences that offer both portrait and landscape views.
To toggle screen rotation, navigate to Settings, Screen Rotation.
Then, make sure the screen is oriented the way you wish it to lock. That is, if you wish to lock the screen in landscape view, tilt the device into that position first. Then, toggle the Autorotate Screen option to Off.
To reverse this effect, simply toggle that option again later.
Note: Since Microsoft did not build this feature into a universally-available user interface, it should have provided a way to Pin this feature to the Start screen, as it did with Driving Mode.
I'll be looking at more new Windows Phone 8 Update 3 features in the days ahead.