For most car's GOFAR is 99+% accurate with reported fuel consumption figures.
However for for some cars (that do not have a MAF sensor*) and diesel vehicles there can be an offset in the fuel usage reported by GOFAR (due to the way the computer calculates and reports the engine data).
It is important to note that even the reading on the dash computer will not be 100% accurate in these cases also.
GOFAR has a feature to adjust for this offset so that you can ensure that you get accurate fuel consumption data even with diesel engines and cars without MAF sensors.
In settings you can find the feature called 'Fuel Trim' that allows for you to adjust to this.
You can find this in Settings -> Vehicle -> Edit Car -> Fuel Trim
Let’s say for example that GOFAR is reading 5% higher than the actual fuel usage. You can set the fuel trim to -5% to compensate for this.
If you would like to be very accurate with this, you can do a mileage check by doing a tank refill and recording the km and working out the actual mileage. Then compare that number with the GOFAR data over the same period and calculate the real the offset. Then just enter the adjustment into fuel trim feature. For best results be sure to do the test under your normal weekly driving conditions.
* MAF stands for Mass Air Flow