The relative strength index (RSI) was introduced in 1978 by technical analyst J. Welles Wilder Jr. in his book New Concepts in Technical Trading Systems. The relative strength index is a momentum ...
However, in practice, due to the way the formula is calculated, the RSI will rarely go higher than 80, or lower than 20. It is therefore much more common to use the levels 70 and 30 for trading ...