I weigh almost every morning, post 2-minute piss (not like I could do it before that anyway). I call this my "dry weight". The only way its more than a pound or so different than it was the day before is if I had a good bit more or less sleep that night, or if I ate a lot more or less than normal for supper the night before. Over the course of a week I can see if I'm going in the right direction, but two or three days is meaningless.