Liters and gallon units

I would like to add Volume Units on Units & Values.
The units are L > gal (US) > gal (UK)

Internally this is already in use per the ‘Fuel Consumption Display’ selection. Could you describe the situation where separate setting is needed?

Can be used as displaying calculated values Trip A, B and Current Fuel Consumed on Trip Info like average fuel economy, average and max speed, fuel consumed, fuel cost etc.

But that already works by changing fuel consumption units at the settings.