Relative Strength Index (RSI)

A popular oscillator developed by Welles Wilder, Jr. and described in his self-published 1978 book "New Concepts in Technical Trading Systems". RSI is plotted on a vertical scale from 0 to 100. Values above 70 are considered overbought and values below 30, oversold. When prices are over 70 or below 30 and diverge from price action, a warning is given of a possible trend reversal.