While googling on a boring afternoon I find pics of what appears to be a glock select fire device. I'm staring at it for about 15 minutes and have no idea how it works. I know the little stationary post presses down the cruciform when the action closes but how that switch selects firing mode is giving me a headache. Obviously that switch rotates the cam on the other side but what would that do? Wanna kill these ads? We can help!