this is GREAT for learning - and for some debugging operations too - but just do NOT try it on an operating "production" system ... remember the processor is only looking at ONE rung at a time - so the machinery can do all sorts of unpleasant things ...
watch the red "cursor" as you click the button ... and with most systems, you can right-click and "toggle" the inputs off or on just before you "trigger" a particular rung into execution ...