Gas Mileage

I've been tracking the gas mileage of my car. Such a simple thing really. My Dad used to have a little notebook where he entered the odometer reading, and the gas that he purchased. I picked up the habit, but never did anything with the data since it was on paper. (I often wonder if Dad did anything with his data.)

So now I have an Excel spreadsheet which calculates days and mileage between fill-ups (it's at 27MPG). In addition, it records which gas station I used, and how much I spent per fill-up, per gallon.

What is the biggest thing this exercise has taught me (besides stop using paper to record mileage)?

I now understand how much gas I have left whenever the gas light turns on. This light appears whenever the fuel tank is 'low'. The Audi A4 that I drive (1.8T FWD) has a 16.4 gallon fuel tank, and the most I have ever filled up my car is 14.4 gallons. The light seems to come on whenever I have two gallons left, and that gives me a little over fifty miles before I need to get gas again.