Hi Robert,
Just thought I would come back to this one for some closure. After a couple of partial fill-ups the car has now beem brimmed for the first time in a while, and the data doesn't look out of place.
I would assume a missed fill-up would cause a large spike in the mpg graph, and there isn't one.
I think I'll have to put this one down to age...
Sorry to have troubled you.
__________________