Good app but dont depend on it.
So..... I downloaded this app in order to see what my real iPad usage was. I wanted to see if my next iPad purchase should have the cell in it or not. (Can I really afford the data plan.) so I downloaded to both my iPhone and iPad to figure out what my general usage would be. It seem me to work fine until the app updated this month, then it dumped all the current data and started over. You lose a star for the lost data, but generally easy to use overall.
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Data Monitor - Manage Your Usage