^
If you'd actually read the DOE study you'd see that they used shop rags similar to what you suggested to simulate dirty filters and even increasing them to the point of noticeable driveability the fuel injected vehicle showed no significant reduction in fuel economy.
And you can't get more precise than the outputs of the odometer and pump volume. My pump gives me gallons to 3 digits I assume your pumps gives imperial gallons to 3 decimals or liters to 3 decimals? My odometer miles to 1 decimal, I assume yours gives kilometers to 1 decimal. We both deal with 4 significant digits so I can comfortably publish my mpg to 2 decimal points, and you can express to 3 decimal points with L/100km, but 4 significant digits is equally precise. Sure if you pump tells you liters it is technically to 1/10 of a smaller volume and kilometers are shorter than miles so I'll give you that it could be more precise.
Of course if your pump goes to 2 decimals I take that back.
