# Quick-tip 43 | Draw a line at the SetPercentTrailing level

## Draw the SetPercentTrailing level

Quick-tip 43 demonstrates how to calculate and draw a line at the trailing stop loss level when using the TradeStation function: SetPercentTrailing.

This quick-tip program does not take the Commission and Slippage settings into account when calculating and drawing the trailing stop level. Quick tip 43 assumes that SetPercentTrailing is being used on a SetStopPosition basis.

Also see tutorial 80 which looks at using SetDollarTrailing.

SetPercentTrailing is a built-in stop reserved word is used to specify the amount of the maximum open position profit you are willing to lose (as a percent) as well as the profit level that must be reached in order for the stop to take effect. The position is closed out when the specified percentage of the maximum profit is lost.

The reserved word is called using: SetPercentTrailing( FloorAmnt, Amount ); where FloorAmnt is the profit level that must be reached in order for the stop to take effect and Amount is the amount of the maximum open position profit you are willing to lose (as a percent).

#### Notes on the calculation

OpenPositionProfit returns the current gain or loss of the current open position. CurrentContracts returns the number of contracts in the current position BigPointValue returns the market value of a whole number price move for the share or contract price of a particular symbol.

An exit will occur when
OpenPositionProfit = MaxProfit( 1 – PercAmount / 100 )
provided the FloorAmt of profit has been reached

Imagine an ‘imaginary entry price’, iEP (not taking commission or slippage into account)
OpenPositionProfit will be equal to iEP – price at the moment multiplied by CurrentContracts multiplied by BigPointValue.
i.e. OpenPositionProfit = ( iEP – Close ) * ( CurrentContracts * BigPointValue )
re-arranging the formula
iEP = Close + OpenPositionProfit / ( CurrentContracts * BigPointValue )

So at the stop level (STrl2) we can substitute OpenPositionProfit into
OpenPositionProfit = MaxProfit( 1 – PercAmount / 100 )
we get ( iEP – STrl2 ) * ( CurrentContracts * BigPointValue ) = MaxProfit( 1 – PercAmount / 100 )
where the stop (STrl2) is located. Re-arranging the formula
( iEP – STrl2 ) = MaxProfit( 1 – PercAmount / 100 ) / ( CurrentContracts * BigPointValue )
and STrl2 = iEP – MaxProfit( 1 – PercAmount / 100 ) / ( CurrentContracts * BigPointValue )

## Video explanation

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