TFS: Tether Line

/*********************************Provided By:      eSignal (Copyright c eSignal), a division of Interactive Data     Corporation. 2008. All rights reserved. This sample eSignal     Formula Script (EFS) is for educational purposes only and may be     modified and saved under a new file name.  eSignal is not responsible    for the functionality once modified.  eSignal reserves the right     to modify and overwrite this EFS file with each new release.   Description:            TFS: Tether LineVersion:            1.0  09/26/2008Notes:    Tether line indicator is the first component of TFS trading strategy.    It was named this way because stock prices have a tendency to cluster    around it. It means that stock prices tend to move away from the midpoint    between their 50-day highs and lows, then return to that midpoint at some    time in the future. On a chart, it appears as though the stock price is    tethered to this line, and hence the name.Formula Parameters:                     Default:    Length                                  50**********************************/var fpArray = new Array();var bInit = false;function preMain() {    setPriceStudy(true);    setStudyTitle("Tether Line");    setCursorLabelName("Tether Line", 0);    setDefaultBarFgColor(Color.green, 0);    setPlotType(PLOTTYPE_LINE, 0);     setDefaultBarThickness(1, 0);        var x=0;    fpArray[x] = new FunctionParameter("Length", FunctionParameter.NUMBER);    with(fpArray[x++]){        setLowerLimit(1);          setDefault(50);    }}var xTether = null;function main(Length) {var nTether = 0;var nState = getBarState();    if (nState == BARSTATE_ALLBARS) {        if (Length == null) Length = 50;    }    if ( bInit == false ) {         xTether = middleDonchian(Length);        bInit = true;     }     nTether = xTether.getValue(0);    return nTether; }