Extra line appears on plot with startTimer()

[GG2013]

Hallo,
I would like to read & plot data, say every 1 sec (i.e new curve should replace the old one). I have plotted the graph (see attached figure) okay but when I use the timer an extra line (average?) appears on graph. At the moment it's reading the same data every 1 sec but later it will be replaced by new set of data.

Any idea why the extra line appears, and how to remove it?
Thank you.

Screenshot.jpg

Plot::Plot(QWidget *parent ): QwtPlot( parent )
{
….
…
    (void) startTimer(1000);// 1 sec
 
    //populate(); //this works fine
 
    connect( legend, SIGNAL( checked( const QVariant &, bool, int ) ),
        SLOT( legendChecked( const QVariant &, bool ) ) );
 
}
 
void Plot::populate()
{
….Read data from a file…..
 
    for ( int c = 0; c < 3; c++ )
        data[c].curve->setRawSamples(&timeData.front(), &yData[c].front(), timeData.size() );
 
}
 
void Plot::timerEvent(QTimerEvent *)
{
    populate(); //Getting data for plotting
    replot();   // to refresh plot
}

Plot::Plot(QWidget *parent ): QwtPlot( parent )
{
….
…
    (void) startTimer(1000);// 1 sec

    //populate(); //this works fine

    connect( legend, SIGNAL( checked( const QVariant &, bool, int ) ),
        SLOT( legendChecked( const QVariant &, bool ) ) );

}

void Plot::populate()
{
….Read data from a file…..

    for ( int c = 0; c < 3; c++ )
        data[c].curve->setRawSamples(&timeData.front(), &yData[c].front(), timeData.size() );

}

void Plot::timerEvent(QTimerEvent *)
{
    populate(); //Getting data for plotting
    replot();   // to refresh plot
}

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