Scan Gauge 2

We just took our maiden voyage in our new-to-us 2008 Winnebago Chalet (Ford E-450 chassis) and were talking during the drive about getting a ScanGuage II. One question that we discussed: is there any sort of accomodation or override for generator use when it figures out MPG since the genny fuel comes from the vehicle fuel tank? (or likewise, how would you manually figure that out of your MPG if you're keeping track on paper?)

Cheers!
Kristin