Man, that's the worst feeling. One bad pour from eyeballing it and you're scraping sand out of a mold for hours. The scale just takes all the guesswork out, even if it feels a bit fussy at first.
Yeah, that "scraping sand out of a mold for hours" thing is brutal. My buddy had a whole batch fail because his scale battery died mid-measure and he didn't notice. Guess who was redoing everything on a Saturday?
Remember it's not just about weight for sand cores. The real trick is the moisture content. You can weigh your sand and binder perfectly, but if your sand is too damp from humidity, the whole mix is off. I learned that one summer when every core was soft, even with careful weighing. Now I keep the sand sealed up tight and test a handful for feel before I even start.