Apple iPhone - Lock Aspect Ratio

If you want to stop your iPhone from rotating the screen when you move it sideways, you need to lock its aspect ratio. Here's how:

1. Double-tap the home button (press it twice quickly). This brings up a row of app icons.
2. Swipe this row right, so the icons located further left come into view.
3. On the left hand side you should see an icon that looks like a arrow pointed around on itself. Tap this icon and you should see a lock appear in the middle of it.
4. Tap the main screen area or the home button to exit.

Now you should see a smaller version of the aspect lock icon near the top right of your screen, next to the battery indicator.

To undo the aspect ratio lock, do the same thing again to remove the lock icon.