most discussions on FC centre around the number of kilometres that can be driven using one litre of petrol, ie xx km/litre
since the system is reporting in litres/100 km, eg, AA litres/100 km, divide 100 by this number (AA) to give the result in km/litre
for example :
if the system shows 7 litres/100km, divide 100 by 7 = 14.2 km/litre
and 8 litres/100 km = 12.5 km/litre
enjoy your drive