I think the best way to describe the gas gage on the Prius is nonlinear. If your commute is like mine, about 10 minutes with no highway time and a number of lights (I bet there are very few here that can share that experience), then you often find that the fuel gage hovers on a pip for many days (more than a week) without droping, and then it will drop 2 pips in a week and then hover again. I've been hovering on 3 pips for at least a week and half now and I keep wondering when it will drop to 2 remaining.

As a general rule, I fill up at 2 pips regardless of how many miles I have traveled or how much farther my average indicates I can go. I get between 7 and 9 gallons of fuel into the tank when the gage shows 2 pips.

It has been said:
Hybrid drivers come in 3 flavors, greenie, techie and cheapie. Pick any 2.
2005 Prius, Melinium Silver over gray, package 5 (AI)