Bollinger-Bandwidth-as-Standard-Indicator

Boy, I don't know how I missed that. Now I've got it! Thank you!

Apparently, Post #1 is right. I ran a comparison below. Notice how the blue (BBWidth) and orange (Built BBWidth) plots superimpose very nicely below within 2.5 decimal places. You taught me something.

CODE:
using WealthLab.Backtest;
using WealthLab.Core;
using WealthLab.Indicators;

namespace WealthScript3 
{
   public class MyStrategy : UserStrategyBase
   {
      public override void Initialize(BarHistory bars)
      {
         IndicatorBase bbWidth = BBWidth.Series(bars.Close, 15, 2.0);
         
         IndicatorBase bbLower = new BBLower(bars.Close, 15, 2.0);
         IndicatorBase bbUpper = new BBUpper(bars.Close, 15, 2.0);
         TimeSeries bbWidth2 = (bbUpper - bbLower) / new WilderMA(bars.Close, 15) * 100.0;
         PlotTimeSeriesLine(bbWidth2,"Built BBWidth",bbWidth.PaneTag,WLColor.Orange,6);
         
         PlotIndicator(bbWidth,WLColor.Blue);
      }

      public override void Execute(BarHistory bars, int idx) { }
   }
}

Just understand that any indicator based on the standard deviation is going to blowup if it hits an outlier. Basing the width on a "robust" indicator such as the median, percentile rank, or even ATR would be much safer.

If you're interested, WL has KeltnerLower and KeltnerUpper bands available that are based on an ATR multiple. You can substitute those into the above code to compute a KeltnerBandWidth if you want to try that out. It should be more robust in the presence of outliers.

Just understand the KeltnerLower and KeltnerUpper bands employ the SMA (rather than the WilderMA) as their center line follower. I personally like the WilderMA a little better. If you prefer to employ the WilderMA as your center line, then WL has ATRBandLower and ATRBandUpper indicators that let you define your own center line (such as the WilderMA) you can use instead of KeltnerLower and KeltnerUpper.