Calculator Configuration of Total Field

Hello,

Problem:
Sometimes the information the client needs in the total line is sum, sometimes the average and the platform have different configurations over this, sometimes doesn't appear anything, sometimes the value of the first line.

Solution:
In calculator, create an option to choose between average, sum, max and min.

A case where I need this:
A client asked for calculating the percentage of fuel that have in the tanks of the vehicles in a determined group of vehicles.
We are using summary report with final fuel level colummn, custom field with the tank capacity, the formula: FINAL FUEL LEVEL.const100/custom_field(Tank).

We need to have the sum of the whole final fuel level and the whole custom field in the formula.
The client wants this info to know how much fuel he have inside the vehicles to control his fuel demmand.