In Starcraft 2 I can set my mouse sensitivity to some percentage value. What does 100% mean? Is 100% my Desktop mouse sensitivity or the fastest possible speed for my mouse?
I want to have the exact same speed as I have on my Desktop.
The 100% refers to the maximum speed that Starcraft 2 will move the pointer.
At 50% (with no pointer acceleration) for every one mouse count your computer will move the pointer one pixel on your screen, a 1:1 ratio.
While the slider may read 50% it may actually be set to 49.5% instead. However windows only recognizes 20 different mouse settings which correspond to 5% intervals so this value is rounded down.
By setting SC2's in game sensitivity to between 51%-54% one can ensure that SC2 will be utilizing a 1:1 ratio exactly.
As Ampersand says, disabling "Enable Mouse Sensitivity" results in Starcraft using the OS mouse settings and not the internal SC2 settings.
info/source, some of it cut and pasted from: Liquipedia II
If you want to use desktop mouse speed, you should uncheck "Enable Mouse Sensitivity" under Options -> Controls.