This uses a Rescaled Range from Benoit Mandelbrot's Misbehavior of Markets to devise a Risk Range on stocks. A trading position can be managed by selling portions at the top of the risk range and selling at the bottom of the risk range.
The Length parameter defines how wide the range is and how frequently the price will reach the range bands.
The Vol Length Parameter defines how far back to weight volatility, and how responsive the bands will be in response to volatility