This indicator is based on Historical Volatility.
It's plot the simple moving average with a upper and a lower band.
The bands are calculated like this:
UpperBand = 20 Simple moving average + 20% * Historical volatility
LowerBand = 20 Simple moving average - 20% * Historical volatility
But, you can change the paramters. I use the 200SMA with 100% of Historical Volatility either.
How to use:
If the price are negociating out of the bands, it's dangerous to trade this stock.
Hope you like it.