'85 4k quattro/trip computer accuracy

[mark wolfson]

Please tell me if it is possible to correct an innacurate trip computer. It is reading an average of 27+mpg per tankful, when I am actually getting a little over 19mpg combined. All facets of computer seem to work, but if the top mpg is an average of the whole tankful (without resetting inbetween trips), then this thing is way off. Anyone out there with the experience of dealing with this thing? If it is inaccurate, are there any baby-boomer Audi technicians who know this car at a dealership? Mark