AWOL, oops! Thanks.
Geoff: Yes, it can be assumed to be a cylinder. That would be the easy way out. I was attempting to only display the gallons in 1/4 gallon increments though. While the measurement taken by the US will be a large range. I used inches as an example, I actually have the system outputting millimeters. The system will measure 0-199 millimeters, before the system recognizes it as 0.25 gals. Then it would read 200-399mm as 0.25 gallons.