If my display is only 0.3% off I will not bother to correct anything as that is close enough for me. I hear the HCH is off by 10 times that amount or a full 3% which is starting to be a big enought difference to worry about. At a full 10% off my Vette's display is useless without a correction factor. These things use so little gas that it is going to be a while before 5 tanks go into the database.