Creating a bandwidth report

Hi, I am writing a bandwidth utilization report in SQL and am unable to match the values in the dashboard to the database table.  I am using the InterfaceTraffic table to capture total bytes transferred per hour for a particular node.  The values in this table do not match Total Bytes Transferred in the Interface Charts section of the dashboard.  Is there a different table I should be querying for this information?  Thank you in advance for any assistance!