Odometer and speedo run off the same cable and my speedo is accurate compared to GPS on my phone so hopefully the odometer is correct
Based on c. 3,000 miles in my ownership over a bit less than 3 years I've averaged 39mpg = 14km/litre = 7l/100km (take your choice of measurement). That seems to be in line with
@AndersLS and
@smart51. Mine's a 499c standard engine btw.