Accuracy of Gas station pump

[benfrogg]

So, in recent months I've been noticing that my MPGUINO display has been getting farther away from my actual. It started about 2 mpg lower than the display said. For instance, if it says 64mpg, actual would be 62. The last several tanks, it's been going down. Each tank it seems worse when I still get the display to read 64-65mpg. This latest tank the reading was 58.82 whereas the display read 64.11.

What can be to blame here?
New gas tank, 4 months or so ago. No leaks. No fuel odor. Fuel cap holds pressure (gasket in good shape, hisses when opened after the tank has been depleted). No change in driving habits. No change in type of driving.

Temps have changed, but not significantly. It was averaging the 20s last month, it is averaging the 30's now, sometimes 40.

I have used the same pump at the same station for several months. Only thing I can think is that the pump is off. The theoretical reduction in actual fuel dispersed coincides directly with the price of fuel going up..... Mobil station......

I know thermal expansion is a possibility, but I'd assume that would work out over time.
Ideas?
B