Use the weider HSV, it has a digital fuel gauge in interior view accurate to 0.1 of a litre. Just fill it one litre below the recommended amount, and if you're still over just reverse back and forth until you get there.
P.s the fuel gauge works backwards, so it tells you how much space is in the tank. I.e full tank shows 0, and empty is 99.9
P.s the fuel gauge works backwards, so it tells you how much space is in the tank. I.e full tank shows 0, and empty is 99.9