True Strength Index
The True Strength Index (TSI) is a momentum-based indicator developed by William Blau. The TSI is suitable for intraday time frames as well as long term trading and helps to define trend and oversold/overbought conditions.
The formula for TSI is:
TSI = ExpMovAvg(ExpMovAvg(NetChange, Long),Short) / ExpMovAvg(ExpMovAvg(AbsNetChange(n), Long),Short)
Long = Long Period
Short = Short Period
NetChange = Price - Price 1 bar ago
AbsNetChange = Absolute value of Price - Price 1 bar ago
s is the short period which must be an integer.
l is the long period which must be an integer.
A True Strength Index 3, 9 can be written as follows.
XAVG(XAVG(C - C1, 3), 9) / XAVG(XAVG(ABS(C - C1), 3), 9)
Read more about True Strength Index (TSI) at Investopedia