Tunable TO WHAT? What you think your mileage should be? Even if you adjusted it to the number a long term "old fashioned" calculation gave you there is no guarantee the next one would be the same and certainly 0.5-0.7 is well within the margin of error. There are so many variables that effect gas mileage that it would be impossible to get the accuracy you claim on the fly without a sophisticated PC measurement system with actual flow meters in the fuel lines, accurate temperature measurements and dead on distance travelled. Even then it's going to have to be averaged because it's never going to be repeatable.