true estimate is that in which we attach a 100ml petrol bottle with bike,, and empty the carb,, the will give accurate reading in that particular environment,, u can test ur mileage on straight road separately,busy city traffic separately,and on uphill separately,downhill separately,,or mix riding,
the reserve method is also ok but a bit inaccurate cause there is still some petrol left in the carb and reserve may be hit even if there a bit more petrol in the tank as the bike may not be at plane surface all the time,,
also note that the 70cc carb float contains approx 20cc petrol which makes it run for 1 km,,