Only 1 band is plotted at all times depending on the bias of the trend.
Default settings are a 21 as a centerline with a 13 period ATR.
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.