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# True Strength Index (TSI)

## Description

The True Strength Index (TSI) is a momentum-based indicator, developed by William Blau. Designed to determine both trend and overbought/oversold conditions, the TSI is applicable to intraday time frames as well as long term trading.

## Syntax

`TSI(int fast, int slow)`

`TSI(ISeries\<double\> input, int fast, int slow)`

**Returns default value**

`TSI(int fast, int slow)[int barsAgo]`

`TSI(ISeries\<double\> input, int fast, int slow)[int barsAgo]`

## Return Value

**double**; Accessing this method via an index value `[int barsAgo]` returns the indicator value of the referenced bar.

## Parameters

| Parameter | Description                                                                                     |
| --------- | ----------------------------------------------------------------------------------------------- |
| fast      | Period of the fast smoothing factor                                                             |
| input     | Indicator source data ([Series\<T>](/developer/desktop-sdk/references/common/iseriest/seriest)) |
| slow      | Period of the slow smoothing factor                                                             |

## Examples

```csharp
// Prints the current value of a 20 period TSI using default price type  
double value = TSI(20, 10)[0];  
Print("The current TSI value is " + value.ToString());  
   
// Prints the current value of a 20 period TSI using high price type  
double value = TSI(High, 20, 10)[0];  
Print("The current TSI value is " + value.ToString());
```

## Source Code

You can view this indicator method source code by selecting the menu New > NinjaScript Editor > Indicators within the NinjaTrader Control Center window.