I think both methods are widely used. It's just whatever works best for YOU. Like Deborah said, the easiest way is to eye-ball it. I can't disagree with her, but she has a LOT more experience than I do. I "think" I could eye-ball it and be okay, I'm still new and like to weigh as a way of double-checking myself. The past few weeks though, I've done more eye-balling and less weighing. It's just what you feel comfortable with.