If the setup parameters for your vehicle are not in the table of car settings  then you should do some calibration to ensure the readings will be accurate. Please add your findings back to the table of car settings for the next person.
Step 1. Go to gas station and fill up. Note what pump you are at, where your car is in relation to the pump, the position of the pump nozzle in the tank, and the number of clicks you use, and even the time of day/temp.
Step 2. Before leaving the station, tap the left and middle buttons together and you should see a brief "tank reset" message", note your odometer reading (assuming your odometer is accurate)
Step 3. Drive around like normal. The more the better, a couple hundred miles at least.
Step 4. Refill the tank, reproduce the conditions in step 1 as well as you can. Bring a calculator and a pencil with you.
Step 5. Before leaving the station, determine the miles traveled since the previous refill based on the cars odometer, and the number of gallons you just pumped in. Then go to the "Tank" screen and note the miles traveled and the gallons used according to the guino. Then tap the right and left buttons once to bring up the setup screen and:
A. navigate to the "VSS Pulses/Mile" screen (hint, left and right buttons will proceed to the next setup value without saving any changes in the current value). Take that value, multiply it by the number of miles the guino said you traveled, then divide it by the number of miles on the odo. Adjust the value to this new value and hit OK.
i.e. newVSSPulsesPerMile = vsspulsesPerMile * guinomiles / odomiles.
B. on the "MicroSec/Gallon" screen, Take that value, multiply it by the number of gallons the guino said you used, then divide it by the number of gallons the pump says you just added. Adjust the value to this new value and hit OK.
i.e. newMicroSecPerGallon = MicroSecPerGallon * guinoGallons / pumpGallons.
C. Navigate through the setup values till you are back at the tank screen. It should now show accurate distance traveled and gallons used for this tank.
D. If you are happy with the displayed tank miles and gallons display then reset the tank with the left and middle buttons and drive on. Otherwise double check your numbers on paper and in the setup.
NOTE: The Mpguino counts VSS pulses, whether moving forward or in reverse, as mileage. How odometers record in reverse seems to vary. Also if you do any EOC with the key off, your VSS may not work, and the Mpguino will not be recording mileage, but a mechanical odometer will continue to work. If your Mpguino shows slightly more mileage than you odometer, one (or both) of these may be the cause. (Don't attempt to calibrate the Mpguino to match the Odometer exactly)