The Stochastic RSI was developed by Tushard Chande and Stanley Kroll and measures the level of RSI relative to its range. Stochastic RSI is an indicator of an indicator. It applies the Stochastic calculation to RSI values (instead of close prices). The result is an oscillator that fluctuates between 0 and 1.
Chande and Kroll explained in their 1994 book, The New Technical Trader, that RSI sometimes trades between 80 and 20 for extended periods without reaching overbought and oversold levels. So to increase the sensitivity and provide more overbought and oversold levels in RSI, they developed the Stochastic RSI.
Stochastic RSI = (RSI - Lowest Low(RSI) for Period) / (Highest High(RSI) for Period - Lowest Low(RSI) for Period)
The default Period is 14.
Relative Strength Index