It’s cool that iPads can sense how you are holding them and orient themselves properly for reading, whether you are holding the device horizontally, vertically, or upside down.
However, there are cases where you want the screen orientation to stay the same even when you turn your iPad over. It’s easy to lock the rotation; just slide the switch above the volume control on the upper right of your device.
One caveat, though: under Settings, in the General menu, scroll down and ensure that “Lock Rotation” is checked. Otherwise, that switch will function as an audio mute switch (which can also be useful).