The computer comes up with it's numbers by measuring injector pulse width and what it is supposed to flow at said numbers vs hours run, mileage, avg speed etc. Some can be close at some points but way off on others. The only way to really do it like a few have said before is checking mileage vs gallons you put in the tanks.
Last edited: Jun 17, 2019
Reason for edit: Me no spell much good.