I needed to eat something so I've stopped in Serbia and decided that I'll fill Berta's tank. I wasn't sure that MPGuino's calibration was accurate so didn't know how much fuel left in the tank. And I've driven for 1558km (968miles) on that tank. I know I could go for 1k miles tank, but maybe next time...
Anyway the pump showed 53,69 liters after topping up tank. Guino showed 53,75 so calibration is almost perfect.
Anyway FE was 3.45 l/100km (68.18 mpg US)!
Best tank ever!