This can be used to monitor for numpad keypresses even when the game is focused. The code for this functionnality can be read in NumpadListener.cs.
When the application is running, it will optionally install a hook that receives every keyboard events in the system. More information and screenshots here: Windows hook This allows you to quickly calculate the elevation for a given distance without alt-tabbing out of the game. By running on the desktop, this tool is able to use Windows hooks to monitor keyboard input. This is a simple artillery calculator for Hell Let Loose that runs on your desktop.