It is possible to fluctuate quite a bit in one day due to a variety of factors. For myself I did a little experiment of weighing in every hour for one day just to see and I fluctuated 8 lbs. some things that I noticed made a difference for me was what/when I ate, my hydration level, if I was exercising or sedentary - things like that. I've read that 5 lbs fluctuation in one day is quite normal (can't remember the source - sorry!). I find if I weight in at the same time of day and under the same conditions, I get the most accurate measure of my weight loss progress.
