Actually the process you describe - taking measurements first so that you have an idea of what's happening as you then adjust by ear - makes a lot of sense. Perhaps that should be differentiated by calling it "educated tweaking", as opposed to "magic 8-ball tweaking". If nothing else, taking the measurements can get you into the appropriate ballpark - it's easy to be twiddling a setting back and forth between 11:00 and 1:00 when you need to be between 2:00 and 4:00 but your preconceived notions don't let you go there. I've sure done that.