Originally Posted by Orcrone

Spiff,

I don't have the NAV system, but I would suggest the manual method. True, you don't know what level the tank was filled to when you received the car so it makes sense to leave out this tank if you want. It's also true that differences in when the pump shuts off may not give you the most accurate measurement for the tank.

However, if one tank reads high because you did not fill up all the way the next one will read low. Even though each tank could be off, over a number of tanks this should give you the most accurate measurement.