I've started monitoring mine as well, and Cox is always double what my router shows, but they are happy to quote
the Cox Data Meter has been tested for accuracy by Cox, as well as Netforecast. Netforecast is an independent third party, and they have provided an independent report verifying the accuracy of our meter. Please see their report below:
Which doesn't tell me anything other than they certified their meter 2 years ago for accuracy. Next time I get pulled over for speeding, maybe I can tell the cop, 10 miles ago my gps can verify I was not speeding, so his radar gun must be mistake.
