Interface History Aggreation

When I have an Interface History widget I have added to a dashboard, is it the aggregate traffic over that interface?  What I mean is I am graphing my Internet uplink and I want to know if the numbers on that graph include all of the VPN tunnels that terminate on that interface?  So is it "additive" of truly all traffic or is it just what goes through the logical interface and I have to add things up myself.