Unfortunately, it can't be fully accurate in the HX. The engine has a lean-burn mode which uses less fuel, but the Scangauge doesn't know about it. The OBD port doesn't report anything about it, so the SG can'd adjust for it. It has to use airflow to calculate fuel flow, but when the fuel-air mix changes, the math is wrong.
The MPGuino project here will read the fuel injectors directly, and report accurate numbers.
For the record, I have my DX set at +12% fuel offset (lower mpg).
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11-mile commute: 100 mpg - - - Tank: 90.2 mpg / 1191 miles
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