I bet when cutting up a big piece of fish or meat you can eyeball the ounces pretty good. I do pretty good at eyeballing calories, even from a picture, unless the scale is hard to determine.
Part of that comes from cutting up thousands of pieces of bread dough and weighing them for when I want 1.5 or 2.0 ounces of dough per serving.
You don't get a choice but to get good.
/johnny