I agree with rp123. If I, for example, drive my GCL on the highway, I'll average 22/23 mpg (I set the cruise control at 78 mph). With 22/23 mpg you'll average over 400 miles on a tank of gas (the tank holds over 20 gallons - I think it's a 23 gallon tank?). The next fill up, the range will shoot out a number over 400 miles. If I drive strictly city, my mpg's are around 16/17 mpg. If I burn the tank with all city driving, my range kicks out something approximately 350 miles. Basically, the mpg you averaged on your last tank of gas is reflected after a fill-up for your new tank of gas.