Is the gas gauge linear?
 

What I mean is I'm at the 3/4 line and I have gone 200 km so will that mean I should get 800 km on my taank? I know gas gauge is only a rough estimate due to the shape of the gas tank but I wish they were more or less linear.

Most taper off at the bottom, hence gauge falls more rapidly near the end. Anyone know?

No, it's not linear. Most (if not all) cars are not linear. Fuel gauges are slow to drop at the end of the ranges (Full and Empty) but drop quickly in the middle. There is a small reserve when reading empty.

This was done because most car owners are idiots. Studies found thet people wanted to see the fuel gauge stay at full longer because it made them feel like that car got better fuel economy if it didn't drop right away. They also wanted to have a little extra fuel when reading empty . They felt running out of fuel just as the needle hits Empty was dumb.

Cool article to read about why manufacturers do that:
Technologue - Fuel Starvation - Motor Trend Magazine

Now did they design the shape of the has tank to do that?

If that is so, does anyone have aschema blueprint of the gas tank? That way i could mathematically determine roughly how much gas should be at the fuel divisions.

Of course I could experimentally figure it out by filling up at the fuel divisions.

I also thought about getting scangauge 2 but even that isn't as acurate as I thought. Although it would be nice to know the instantaneous mpg at times.

Okay roughly figured out that half way on gas gauge is halfway in tank. I figured this out by filling the tank up when I reached half, it filled with just under 26 liters, and since the capacity is 53 liters it is pretty close.

I get almost 400 km at the halfway point. So far better than posted mileage for this car.