Driver information computer and avg. m.p.g.

I have been checking my fuel mileage(3 times so far) on the HHR and each time the computer gives about 1 mpg> more than what I figure. That's not
too much of a difference, but am wondering which is the more accurate? I would think that the computer would do away with differences in the fuel pump at the stations you use and maybe be better to go by.
--
Paul O.
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I've found that the average fuel economy reported by my 02 Impala's DIC is very optimistic compared to reality (2-3MPG more). I tend to fill up at a few different stations around the area here and the trend is the same regardless of the station.
FWIW.
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Not on my 07 Cobalt! The computer is always higher conflicting with actual calculated mileage; miles driven divided by gas consumed since previous fill up. I also find this inaccuracy (?) for the Range number. In reality I would not expect GM to set it lower!
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Paul O. wrote:

Unlikely there are any pump differences. It is very tightly controlled by state and federal regulators unless it is a non retail site. Inventory reconciliation is mandatory.
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Paul O. wrote:

Corvette DIC runs within a couple of tenths (+/-). Buick DIC about .75mpg better than calculated when I drive--lots of miles on cruise control. ... .5mpg worse than actual when my wife drives --short trips. GMC DIC about 1.5 mpg optimistic.
Punchline: all things are relative and -- YMMV. -- pj
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My 04 Impala is consistently 2 MPG higher than reality, regardless.
My 07 Equinox seems to be dead on - without considering tenths.
Willy
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I've found both my cars to be optimistic by 1 -2 mpg. One is GM, the other is not.
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