I currently drive a 2012 SE 2.5 L Camry. Recently, I drove about 250 miles at close to 60 mph. The computer read out 39.9 mpg. It was climbing consistently, and I know would have done better with a few more miles driven. However, I checked it manually once before, and the computer was about 1-2 mpg higher than I calculated. I have owned a Chevrolet Malibu and a 2010 Camry, both with MPG computers. Each of them was 1-2 mpg over my calculations on a regular basis. I try to stop pumping gas when the pump shuts off automatically, so the fillings are relatively consistent. I discussed this and other factors with an on-line moderator at CR, and he discounted such things as temperature and how high the pump's pouring pressure was [differing pressures would make a difference in its automatic shut-off, and temperature would make a difference in fuel expansion, but he wouldn't agree that it was a factor]. Nevertheless, anything causing us to be aware of our driving habits in relationship to the cost of driving is a good thing. Perfect accuracy is not necessary if we are caused to do the right thing by the info we get.
I traded a 2011 Hyundai Sonata LTD 2.4 L for this car. According to the computer, it got 41.2 and 42.1 mpg on several occasions. I think that my Camry will at least equal that. Some trade offs here due to amenities galore in the Hyundai, but I'm happy, and enjoy being back in a Camry.
By the way, it seems to me that the digital and the analogue needle meters are redundant. I would like for the analogue to suggest the current at-the-moment economy of my driving rather than the average mpg.