Outta gas again

[DrG]

Does anyone have any experience with how acurate the infomation center readout is for "Fuel Used"? Today, I ran out of gas again today when the fuel used said 30.5 gallons and I had added an extra 1.3 gallons (long story) the night before so I should have had at least 2 gallons left. It appears to me that the "fuel used" is low and the "average econ" is about 0.5 mpg too high. Oh yeah, I think the speedo is fast too. Can any of this be calibrated?
And then from the "when it rains it pours" department, when I got gas in the H2 today, I started it and shut the door while I put away the gas can and the doors locked WITH the engine running. Hello OnStar, no I don't know my pin number. Gotta get that extra key made.
David