hello, first, I am new to this forum. Seems like a great resource! I am looking into getting an obd2 scanner such as kiwi, ultraguage,scanguage, etc. My main question is this: I am a teen and I only get so much money for gas each week, meaning that I don't ever have enough to fill my tank up. I do know that if you do not enter a tank size on whatever device you are using that it still gives an mpg rating. How far off is this reading? I have heard up to 10%. Now if I enter my tank size, and do not fill my tank up, will this change the reading at all? What have you guys experienced with partial fill ups and the accuracy of mpg readings?