Questions about fuel mileage display on a 2010 toyota corolla

[EthanWalter]

I have a 2010 toyota corolla that has about 180,000 miles and has served me well. However, I've noticed that the gas tank capacity doesn't go as high as it did when I first started driving it. I remember filling up the tank and seeing the projected miles at 400-410. At some point, I noticed that filling the tank would result in projected miles at 345-355. Has anyone experienced this or know why this would happen?

Also, I've monitored my projected miles and noticed that once the warning light goes on, the projected miles seems to drop more rapidly than you'd expect. On one occasion I even saw the projected gas mileage drop straight from 14 to ZERO. Has anyone seen anything like this happen?