This is the highest I've seen

Click image to enlarge

That's 564 miles, quite possible if you fill at the bottom of the Massif where you could quite possible have been up around 45mpg though the readout may have been in the high 30's. The vagaries of the FL average consumption is biased to the last average rather than an average average therefore distance to go will be based on that unknown figure  my PC is slightly to the right of Genghis
2012 HSE SD4 In Orkney Grey now gone, best car ever.

The range can vary hugely depending various factors including the angle of the car (i.e. pointing up or down hill or sloping sideways) presumably due to the position of the sensor in the tank, your previous average and your current consumption. So if you were on the top of a mountain and drove down to the bottom when gravity was the fuel you should get a massively high range.

J

I appreciate how the range figure is worked out but that picture was taken about 40 km after I filled up, it varied between 810 and 900 km over that 40 km

It was slightly unusual insofar as I went straight onto a 90 kph limit dual carriageway for the first 20 km and then kept at 105 kph for the next 20.

I got 6.6l/100 km (42.8mpg) over that 40 km