Originally Posted by jondrew
I have a silverleaf VMSpc and the only way I know to calibrate it is by filling your tank to a known level and dividing the gallons into the miles driven since the previous fill up. Then you can set a calibration factor. So it's only as accurate as that calibration.
That's true. But, it takes several fills and hand calculations to get it accurate. I finally have mine set to less than 1/10 of a mpg difference from actual calculation over a 2000 mile distance. I had to modify the factor several times to get it that close. Now, I trust that what it's telling me is accurate.
FWIW, the OEM mpg gauge reads 35-40% higher than actual.