> For the complete documentation index, see [llms.txt](https://guide.traderevolution.com/project/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://guide.traderevolution.com/project/web-platform/technical-indicators/trend/si-swing-index.md). # SI (Swing index) The Swing Index was developed by Wells Wilder to assess the direction of a price change and its strength in relation to price swings. The Swing Index uses data from the last two bars in order to determine a possible trend change over a longer period of time. Specifically, Swing Index helps identify moments when investors change their trading behavior - moments when price changes (previously aligned with price swings) begin to move in the opposite direction of swings when a previously strong and consistent group of investors (Bulls or Bears) becomes weaker and short-lived only. Since the Swing Index uses data from only two bars to determine the possible development of a longer trend, it mainly attracts short-term intraday traders who are most interested in short-term price fluctuations. According to the Technical Analysis theory: * a buy signal can be considered when the Swing Index crosses over zero value - the trader can expect a short-term upward price movement - the price is not growing yet, but we have an upward swing; * a sell signal can be viewed when the Swing Index falls below zero - the trader can expect a short-term downward price movement - the price has not yet moved down, but we are starting to have a downward swing. ### Calculation The basic formula for the Swing Index is: Swing Index = 50 \* \[ { Cy - C + 0.5(Cy - Oy) + 0.25(C - O) } / R ] \* (K / T) Where: C = Today's closing price L = Today's lowest price O = Today's opening price Cy = Yesterday's closing price Ly = Yesterday's lowest price Oy = Yesterday's opening price Hy = Yesterday's highest price K = the larger of either (Hy - C) or (Ly - C) R = A variable based on the relationship between today's closing price and yesterday's high and low To calculate R, determine the largest of: 1. Hу - C 2. Lу - C 3. Hу - Lу If (1) is the largest, R = (Hу - C) - .5(Lу - C) + .25(C - O) If (2) is the largest, R = (Lу - C) - .5(Hу - C) + .25(C - O) If (3) is the largest, R = (Hу - Lу) + .25(C - O) T = move limit in one direction ### Main parameters T - move limit value in one direction, default is 300.0 The indicator looks as follows on the chart: