&gt;Why not just always use the more accurate system?<p>Time and cost. Do you count retransmits, drop packets before the customer sees them? If so there is a whole lot more tracking that must occur, that means more cpu power, memory, and storage. In the case of the ISP, it probably means more licensing cost on whatever tools they use to capture that data.<p>What is more worrisome is that utilities have standards set and particular rules they must follow in their measurement systems. Do ISPs? I&#x27;ve seen systems that count all packet sizes as 1518 bytes. If you&#x27;re doing mostly bulk transport that is generally the case. If you&#x27;re a customer and do lots of DNS lookups and other small calls, your average packet size will be below that.