Fuel economy indicated v real in TDCi

[Aus911]

Hi all, I have a 2010 Mondeo Zetec TDCi 120Kw with Powershift transmission.

I have noticed normal use the average l/100km indicates 5.2l/100km.
I always reset the trip computer to monitor this and noticed that the indicated l/100km is usually around 5.2 but when I do calculations of distance/fuel used it equates to approx 6.7 l/100km (approx 67l for 1000km).
Has anyone else experienced this. It looks like the dash is set to sell the car??
Anyone know how to calibrate this to indicate more accuralty?

What "real" fuel economy are people getting in their TDCi Mondeos?