As you see, you can vary by more than 5 pounds in a day. Just pick the same time each day to weigh yourself (I would suggest morning, after "business") so you are using comparable numbers. Track it on a spreadsheet or a site such as MFP so you can see the trend. Because the daily noise of going up and down can hide what's really going on.

another tool that's comparable from week to week is the military body fat estimator. http://www.free-online-calculator-us...tml#calculator

How accurate it is is not really sure, but it is repeatable (you'll get the same results with the same numbers, which isn't always true with calipers).