@Lando
The keyboard sends a scancode like it does for any other key. In this case, it's 0C 0192. The OS decides what to do with it, which for Calculator key and Windows OS, makes Windows consult registry key HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\AppKey\18\ShellExecute and execute that app in the current/last-active session, and if none set it will default to %windir%\calc.exe.