We use a 4-20 mA Tranducer to produce a oil level in inches that we then use to give us gallons in the fuel tank.
We then do a Calculated Field using genericCalc and the formula
A= depth of oil (in the example below it’s reported by Monnit sensor 376596)
231= cubic inches per gallon
36= drop pipe set 6" off bottom of tank
I hope this is helpful and saves you some work.