The Williams %R indicator was developed by Larry Williams to show overbought and oversold levels.
It indicates the level of the Close relative to the Highest High - Lowest Low range for the requested Period.
When the indicator crosses below the oversold line (-80) this could indicate a Buy signal and when indicator crosses above the overbought line (-20) this could indicate a Sell signal.
((Highest High for Period - Close) / (Highest High for Period - Lowest Low for Period) * -100
The Stochastic %K line is the exact inverse of the Williams %R.