you should actually only weigh once a month for a true reflection of weight because it fluctuates that much - Can't remember where I read this but I did... I know we all get weighed weekly but obviously this is for plan.
The fact that weight fluctuates throughout the day and daily is exactly why you are told not to scale hop because it can mess with your mind, you may get on midweek to see you have lost 3lb and then self consciously relax a little through the rest of the week, it can also work the other way.
Oh and not to mention all scales are different, scales at group get calibrated on a regular basis, how many of you do this?!