Than that's the one which is 100% accurate.
My car is 2016 1.8 corolla altis cvti. It was showing 15.5km/l on motorway at 120km/h cruise. I filled petrol from thokar to the brim and refueled at chakri hascol which is at 315kms from Lahore. 18.5 liters fuel filled to the brim. It was giving me 17km/l by fuel top up calculations. Keeping in mind that my car lost some of fuel average at kalar kahar salt range as well.