The script supports two plotting methods; Mirrored and Two Lines. If Mirrored is chosen, the indicator plots the component as a positive number, and the component as a negative number. If Two Lines is chosen, the indicator plots two lines, both of positive values. It is the same data, just visualized differently.
Side note: This is very similar to how the strength (average gain) part in the calculation works. However, the uses the realized range (close - previous close) rather than true range. If we were to use the component of the ATR as the average gain part in the calculation, and the component of the ATR as the average gain part in the calculation, we would get very similar (but not equal) results to the standard . This shows how the ATR and the are related to each other.
In true TradingView spirit, the author of this script has published it open-source, so traders can understand and verify it. Cheers to the author! You may use it for free, but reuse of this code in a publication is governed by House Rules. You can favorite it to use it on a chart.