Had occasion to drive today, in my EX CVT 19 plate down to Banbury from Solihull, a round trip of 71 miles mostly on the M42/M40 with about 2 miles each end on local roads. Kept the speed down on the motorway to around 60-62 MPH
Filled up before i started, so the 'Fibometer' was set to zero.
Now reading 70.8 miles, 57.3 MPG, which I don't think is bad. I noticed that engine speed on the motorway was a tad over 2000 RPM which gives a very relaxed style of motoring.
I accept that the 'Fibometer' may be a bit out, but i would suggest on that style of motoring, not much.
As regards day to day motoring, the 'Fibometer' rarely drops below about 48-50MPG, so more than happy!