When you set the tank size do you use the actual size of the tank as in the manual or do you take a gallon or two off b/c of the pick up location not being on the floor of the tank?

Not sure what you mean by this. The tank capacity is 18.5 gallons, and the amount that's non-usable is certainly less than a "gallon or two." I can confirm that I have pumped 18.3 gallons into my tank before and others have pumped in as much as 18.8 (which accounts for the filler neck, too.)
I suppose if you are worried about running out of gas you could set it to 18 gallons so it would give you a half gallon 'cushion.' I prefer to set the actual tank size and simply not let it get below 50 miles DTE (Distance To Empty.) Actually, at ~18mpg average, 50 gallons DTE means that there should be at least 3 gallons in the tank, so maybe 25 miles DTE is a better "absolute fill up" goal.
Incidentally, one of the cool things about the UG is that if you want to you can set an automatic audible alarm for things like that. So you could set it up to where it starts beeping when you get to a certain DTE.
When do you set "distance" is it being the increment of time thats being measured like mph/kph? or times the wheels turn over times?
:infidel:

Okay, I don't understand that question.
The OBDII computer reports distance traveled to the computer. It also reports speed. It's draws its information from the speed sensor (which I think is in the transmission) and it should be about the same as what the odometer shows (which is why you can't "calibrate" the distance with the odometer.)
IOW, the speed sensor is set so that X number of revolutions = Y distance traveled, and Y distance traveled / Z time = speed. On pre-OBD cars this was done mechanically but on OBDII vehicles the computer does the calculating, and the UG is only reporting what the OBD computer calculates.
The reason you need to calibrate is because most odometers are off, even with stock tires, and if you have non-stock size tires the odometer is definitely off.
Best way to calibrate IMO is with a GPS unit. Most GPS receivers have a trip meter in them, so you set the trip meter on the GPS to zero, then set the trip meter on the UG to zero. Drive for a while and then compare the two (the UG instruction manual explains how to do this.)
Some will argue that a GPS is not 100% accurate, either, and that's true but it's "close enough for government work" as we like to say in the government.

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