Thanks! I wanted something that would have some merit, require no special route or rally staff, and be open to all Prius models. It also has to be achievable but only at significant effort. I think I did: true_gallons = indicated_miles / indicated_MPG :: the error is in the tire revs/mile of the tires (*) maximum tank capacity is the limit in the table . . . no need to run out of gas (something I don't care about) no need to overfill a tank (what scares me!) Now there is a cheat, to claim a larger diameter tire. But the requirement to document the tire calibration offset with GPS or mile marker vs. tripmeter makes that a harder fake. Bob Wilson * - I have gone through four distinct tire sets in the 2003 Prius in my 110,000 miles and 9 years and due to an unfortunate pair of punctures, our second set on the 56,000 mile, 2010 Prius, in 5 years. I've also run the tank dry about 30 times in the 2003 Prius and about 6 times in the 2010 Prius so I know their true tank capacity. What I found is the relative 'rev/mile' determines the indicated MPG accuracy and nothing else.