Williams %R, or just %R, is a technical analysis oscillator showing the current closing price in relation to the high and low of the past N days. It was developed by a publisher and promoter of trading materials, Larry Williams. Its purpose is to tell whether a stock or commodity market is trading near the high or the low, or somewhere in between, of its recent trading range.
Williams considered values below -80 as oversold and above -20 as overbought. But they were not to be traded directly, instead his rule to buy an oversold was
We use 14 period calculation, with a 30 range (the distance between the middle line and the upper and lower threshold lines)