If you’re familiar with Windows 8 tablets, you know that many come with a hardware rotation lock, which allows you to prevent the screen from rotating when you physical turn the device. Surface lacks such a button, but there is fortunately a nice software workaround.
It’s not obvious.
To access the rotation lock software control, display the Settings pane. (WINKEY + I, or activate the Charms and select Settings).
Now, tap Screen. As you can see, there is a rotation lock button on top of the brightness slider. Tap this to toggle rotation lock. By default, rotation lock is off, meaning that you can rotate the display by physically rotating the device.
Thanks to the many people who tipped me off to this feature.