The way I look at it, if you know you are eating below or around maintenance calories, the low swings are more accurate than the high ones. I have no idea how to decide what level of hydration to consider normal or how to know if you are at that level. Unless the dehydration is so bad it is giving me a headache and I gulp down more than a glass of water after weighing, I consider my weight reasonably correct at the lower end of swings.