I assume you are referencing my excellent math skills. Let me clarify. When I fill up my car, after the low fuel light has popped on, it will usually hold 13 gallons. As I recall, we have 14 gallon tanks. However, my 13 gallons usually lasts 260 miles.
I ran out of gas once, after the low fuel light had only been on for 5 miles, so I don't test it any more. Usually fill up once it gets under a half tank.
