[mrguyorama]

> My gas car (Prius) uses the EPA fuel economy rating to estimate range at full, and is progressively pessimistic as I use up gas in the tank

Do you have more convincing evidence of this because I have used many Toyota vehicles and they do not use EPA figures to do their range estimation, and can be conclusively shown to be using their internally measured "average mpg" figures to estimate range.

[omgwtfbyobbq]

That sounds right. It could just be coincidence that the range estimate for the Prius is close to the product of EPA fuel economy figure and the tank size.

I'm mostly commenting on all manufacturers being conservative with fuel/energy use/metering. Even older vehicles I've had (carbureted pickup truck) usually have a gallon to so left in the tank on empty.