On Windows 8 tablets like the Tobii M-Series you can let the screen automatically rotate depending on if you use it in vertical or horizontal orientation. By default, screen rotation is enabled. If you like to disable it, follow these steps:
1) Swipe in from the right side to open the charms menu
2) Click on Settings
3) Click on Screen
4) There is a slider coming up to change the screen brightness and on top of it is a symbol for enabling or disabling screen rotation. If it is disabled, there is a padlock symbol.
Alternatively for step 1 and 2 you can also press the windows key + i on a keyboard.