Honda is making a big deal about how its new Insight has been designed with less focus on getting the best result in the official fuel economy tests, and more on real-world economy.

Whether or not that is PR bluster is a different discussion, but it does raise an interesting point about how the official figures are calculated.

Watch our video of the Honda Insight

Firstly, they are not measured on the road, but in a lab on a rolling road, and not by calculating the actual fuel used, but the exhaust emissions and from that working out the economy.

The car conducts two routes, over a total distance of just 6.8 miles. All of which is on the flat. The urban figure is measured over 2.5 miles, at a maximum speed of 31mph and an average of 12mph. The extra-urban test is 4.3 miles at speeds of up to 75mph, but averaging 39mph. The combined figure is simply a weighted average of the two.