My FC is around 12.5kml too. On my last pump, I calculated it was around 13 kml.
BS laa... how difficult can it be? on each gas pump, reset the meter to 0 until next gas pump, see how much has been pumped.
distant run/gas pumped = kml
How difficullt or wrong could that be????
Yes, totally agree with you!
I've been doing the same thing for many months (and many years to my previous WRX).
For Latio, I'm constantly getting 15km/L to 17km/L, for WRX, I'm getting 9km/L to 11km/L.
Even not accurate during pumping the petrol into the tank (+-1L, pump by myself to fuel flow out), the fc still within the ranges.
Fuel does not self generate or disappered too much from your tank, and odometer does not add or reduce vastly within every tank you pump in.
So how not accurate is beyond me. This is simple measurement, accuracy is above 95%, especially accurate if you do maintain the measurement tank after tank!