Hyundai Ioniq Hatchback (2016 - 2022) Premium Hybrid 1.6 141PS DCT auto 5d Owner Review

I was surprised to get a computer reading of 77 miles per gallon. Too good surely? So I filled up the tank and ran the car for 400 Miles and filled up again. I calculated the consumption as 74 mpg. The range is more than 600 miles on a tank. This is better than the manufacturers claimed economy figure. Can't understand that, am I going wrong somewhere? It's a lovely car very easy to drive and comfy. Best car I've ever had.