How Much Is a Number?
The Comcast meter reports Gigabytes, which is a binary number not to be confused with the similar decimal number. There is an easy numbers trap that appears to make the two systems the same. A thousand is often referred to as the metric kilo, followed by a million that starts with the same "M" as mega. But in fact these are very different values. The following table illustrates the difference.
Counting traffic by billions of bytes will result in a -6.9% error relative to the meter which uses binary numbers. A negative error indicates that the value is low relative to the standard value. In this case the decimal is underreporting relative to the meter.