Also calculates standard deviation over a shorter window-length/lookback period (of 'n_std_fast' length) and another over a much longer span of periods(n='n_std_slow', > 'n_std_fast').
These are the two dotted lines appearing as bands around the cross-level line.
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.