How-can-I-use-SPY-as-an-indicator-to-analyze-the-overall-market

There are several ways to use an external symbol like SPY in your market analysis.

1. Use the SymbolData indicator to get the raw value of SPY expressed as an indicator.
2. Use the SymbolInd indicator to base another indicator, like a moving average, on SPY.
3. In C# code, use the WLHost.Instance.GetHistory method, or the GetHistory method of Strategy class itself to get historical data for SPY. If you are going to plot it, be sure to use the BarHistorySynchronizer to get a copy of it that's synchronized with the symbol being charted.

The simple C# strategy below demonstrates how Choice 3) works. This strategy doesn't make any money, but it shows how GetHistory works, which is what Choice 3) is about. I tested it with AAPL using daily bars.

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

namespace WealthScript5 
{
   public class SpyROC : UserStrategyBase
   {
      IndicatorBase rocSpy, rocClose;

      public override void Initialize(BarHistory bars)
      {
         BarHistory spy = GetHistory(bars, "SPY");
         //PlotBarHistory(spy, "SPYPane", WLColor.Gray);
         rocSpy = ROC.Series(spy.Close, 20);
         rocClose = ROC.Series(bars.Close, 20);
         PlotIndicatorCloud(rocClose,rocSpy);
      }

      public override void Execute(BarHistory bars, int idx)
      {
         if (HasOpenPosition(bars, PositionType.Long))
         {
            //code your sell conditions here
            if ( rocClose.CrossesUnder(rocSpy,idx) )
            {
               PlaceTrade(bars, TransactionType.Sell, OrderType.Market, 0.0, "market sell");
            }
         }
         else
         {
            //code your buy conditions here
            if ( rocClose.CrossesOver(rocSpy,idx) )
            {
               PlaceTrade(bars, TransactionType.Buy, OrderType.Stop, bars.Close[idx]*1.005, "stop buy");
            }
         }
      }
   }
}