Inverting the idea ...

Recently I traveled with a friend of mind the new Ford Fiesta car of hers. She was telling me about how Ford had designed this car , especially for the Indian conditions and the kind of tests it had undergone before being launched. While I was looking around and discussing what the new features were in car I came across a extra meter reading on the dashboard dial that was neither the speedometer nor the trip meter ( the reading that you typically set to zero before the start of a journey, to know exactly the distance you travel for the particular trip) but a third one. This third dial was actually a meter the reading on which showed you how many more kilometers your car would run before you would need to refill. Depending on the fuel in the fuel tank and the average mileage the car has , this reading would automatically be set and decrement as you run the car. What a powerful , simple and useful idea. While we can use a trip meter in an inverted sense, to know when we would need to refill, by being aware of how much fuel was put in last time, then set the trip meter to zero, etc...Still , a simple inversion of this idea that instead of having the meter increment as you run the car, instead have it to decrement and know how far you are from zero makes it so much more convenient. A simple yet powerful idea. Why did not anyone else think of it before ?