I'm trying a very basic strategy.  When the stock hits the bottom bollinger band buy, and top band sell.  The problem is I can't figure out how to extract the current value from the indicators.  It also gives me the same value.

In initialize I have   _bb = BB("SPY", 20, 1, MovingAverageType.Simple, Resolution.Daily);

And in OnData I have

   Debug(_bb.LowerBand.Current.Value + " " + data[symbol].Close);

Console shows that the Bollinger band value never changes why the sybol value does.  What am I doing wrong?