Errant data? Last Hour vs. Last Day

Errant data? Last Hour vs. Last Day

I am evaluating the NetFlow Analyzer and am seeing some wierd information: When I look at the "last hour" data of one conversation flow, it is showing 45MBs of data. When I switch to "Last Day", it is only showing 4MB for the same conversation. How can this be? Shouldn't the Last Day show all of the data? I have nTop running on another machine and it is showing that the total data for the day is over 189MB (even though nTop doesn't show conversations, I know that the host in question only converses with one other host). Any ideas?

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