How does one score fights, in general?

I have to admit its different to theorize than to actually judge a fight. Sometimes you sit there hoping...no praying that somebody will land one half decent clean punch in the last ten seconds of a round to make your mind up. In a way you have to be sharper as a judge in a 3 or 4 round amature bout. Another great problem is you score three very marginal rounds to one guy and then in the last round the other fella boxes his ears off and proves he's THE MAN and I'm sitting at a lonely stool with a 39-37 scorecard for the wrong fella. Not as easy as it seems!