If you weigh your self everyday, that could be the problem. You are only supposed to weigh in once a week because you weight flucuates 1-2 lbs everyday. Another anwser is clothing, if you wore really light pajamas and a tank top when you weighed yourself once then you wore jeans and a denim jacket the next time you weighed yourself then it wont be accurate because denim weighs A LOT more than like sweats or pajamas.