# 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:

![](/files/-MgF4RB6qRaszJBHEdps)


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://help.za.velocitytrade.com/web-platform/technical-indicators/trend/si-swing-index.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.