This PerfCounter64 counter reports a count of frames marked Yellow and then discarded, in the downstream (network-to-subscriber) direction in the downstream (network-to-subscriber) direction on this specific subscriber flow. An admin uses it to see whether a flow's own policer, configured for that subscriber's committed rate, is actually enforcing the contracted bandwidth rather than passing everything through unmarked. For a flow provisioned with roughly a 587 Mbps committed rate, a rising cmFlowHistoryFMYDN2A on flow entry 30 shows the operator this particular subscriber is regularly pushing traffic past what they are paying for, rather than the port itself being congested.