Our MH has a SilverLeaf computer in the dash. It computes and displays a rolling mpg, an instantaneous mpg and and average mpg for a trip. I find the rolling and instantaneous mpg's to be pretty useless particularly if the terrain is varying, but I zero the trip settings everyday so I can compute the average for the day.
I find that on a RELATIVE basis the computed daily average is highly reliable (it excludes fuel used by the generator and during periods of prolonged idling with the transmission in neutral); I can clearly see the effects of crosswinds and headwinds and of climbing mountains, etc. With a big fuel tank I buy fuel on a rather erratic basis, so the daily computed mpg's provide me with a more regular statistical basis for analyzing engine performance.
