[OH3] Change/remove sign for display in knob


I have an item with a negative value and would like to display it as a positive value in the HABPanel (as a knob).

The value is only less than or equal to 0, so it would be sufficient if the sign is removed or calculated with -1.

Is there an easier way than writing a rule that calculates a display item?

I use openHAB 3.1.0

Thanks very much!