Thanks for your reply. I got it a little bit, but could you tell me more detailly? It's not patented, is it? LOL.
So, if my DPI=800, In--game setting yaw/pitch=9, MouseSensitivityMultiplierUnit=0.02. Then the calculator comes out of 8.726646inches/360 degrees. Base on this, I tried pi/(9*0.02)=17.45329252inches/360 degrees. It seems like that I need to divide this outcome by 2 to get the correct number. Therefore does it mean that the calculation should be inches/360 degrees=pi/[(In--Game Yaw/Pitch)*MouseSensitivityMultiplierUnit*(DPI/1600)].