Hello,
The trip computer that Volvo used in the 850 is said to be one of the most accurate of any manufacturer. The MPG calculation uses info from the ECM as to how much fuel is injected, rather than comparing the fuel gauge with distance traveled (which could throw the reading off if the gas gauge was out of whack). The fact that it is using data from the ECM makes it very accurate. My wife has a 1995 850 Turbo and her computer has always been very true (even when she lets the miles to empty run to zero, the car still keeps rolling:). Anyway, that's my take.
I hope this helps...
Joe S. - Volvo Master Technician
1988 760 Turbo w/274k miles, 1981 242 Turbo w/243k miles
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