Thanks for the reply
I was hoping to avoid driving the route for a full tank because of the error factor. I would have to drive the new route for several tanks to get the average which could take a long time and potentially waste fuel if it isn't "worth it"
I've read some of the MPGuino information and it seems like a cool gadget. However I have made a strict rule (to myself) that any eco mods I do would need to be justified by a ROI. For example currently if my vacuum gauge (driver mod) continues to net me +3 MPG it would take about 7 fill ups (about 2 months) to pay for itself. I know nothing ventured nothing gained but being broke sucks.