Display absolute value in a chart

Hi

I have created a custom entity with two decimal fields. Think of them as Revenue and Discount. The value in the Discount field will be negative or zero, while the value in the Revenue field Always is positive.

I would like to create a Bar chart with Revenue and Discount, but I do not want the Discount Bar to be displayed below the zero line. Instead I would like it to be displayed beside the Revenue Bar to make it easier to compare them.

I have not been able to find a way to get the absolute value of Discount, or multiply the Discount with -1. Is there a way to create my chart?

Regards

Peter