The guess gauges on most cars are non-linear. They move slower when the tank is almost full, and fast when it is below 1/4 tank. I normally go about 120-150 miles before the first bar drops. At the half-way point I have typically driven about 350 miles. Then, it is down to one or two bars when I hit 500 miles. Non-Linear!

Kirby
http://greenhybrid.com/compare/mileage/car/1024.html