Bandwidth usage is measured from samples taken at the switch. You can monitor and check your bandwidth usage by logging into your cpanel. Once there, look at the Bandwidth usage (current month) on your left of the CPanel x2 skin or the "General account information" at the bottom left of the RVSkin rvlightblue theme in question to see how much bandwidth you are using. The total transfer listed is the actual transfer your server has done, both in and out.