Added a superimposed padlock to the blurred screen

I added a superimposed padlock to make the screen less ambiguous and give your eyes something to focus on when you look at it (this was causing me a lot of eye strain). Maybe this would be best as a command-line toggleable option?
Oh. scale=4 is a parameter for bc to tell it to use floating point (up to 4 places). If you don't do this, it will round everything to integers at each step and output 0.