This app used to be quite accurate, and I have used it for about one year. Lately, however, it seems to bi going off the rails. I will open it up and discover I am suddenly half way through my monthly quota, then when I check what it says against what my carrier shows, I find out I am nowhere near the halfway mark. I constantly have to go into the app and adjust it to get back on track. Hopefully it will get fixed as I used to find it very reliable.
landryh about Data Monitor - Manage Data Usage in Real Time, v2.03