I have an 04 HCH, I use the actual data from the pump and odometer and I keep a meticulous log. Remember, the OSD shows a converted (from metric) reading. The MPG estimate jumps in .4 and .3 increments as that is what the rounding from the conversion delivers.

So, when your gauge reads 63.2 mpg, it could be as low as 63.05 or as high as 63.35 which is halfway to the next lower and higher increments.

I agree, I see about a 5 percent more ambitious reading on the gauge than the manual results compute.

My lpmg, as read on my Trip 2 gauge (never reset) is 54.1 my actual, via calculation, is 52.4.

Hope this information is useful.

-Charlie...