I have been using this app for a couple years now and it has been incredible. I got the premium version for I believe $1.99 or 99¢, but either way it has been worth it for me. It is has a very simple, easy to use design, and it helps me track and understand my fluctuations. This app is a must have if you are trying to gain, loose, or maintain your weight. The milestones are also very helpful and motivating. It also allows you to transfer your data via drop box and integrate with the health app. 100% recommend.
BeijanOne about Happy Scale: Simple Weight Loss Tracker with Daily Moving Average Trend Line, v4.5.1