Elapsed Time on a QLabel. How to do it?

[GuangZor]

void MainWindow::updateETLabel(){
        QString text = QTime::currentTime().toString("hh:mm:ss");
	setETLabelText(text);
}
 
//MainWindow constructor:
ETTimer = new QTimer(this);
connect(ETTimer,SIGNAL(timeout()),this,SLOT(updateETLabel()));
 
//StartButton:
ETTimer->start(1000);

void MainWindow::updateETLabel(){
        QString text = QTime::currentTime().toString("hh:mm:ss");
	setETLabelText(text);
}

//MainWindow constructor:
ETTimer = new QTimer(this);
connect(ETTimer,SIGNAL(timeout()),this,SLOT(updateETLabel()));

//StartButton:
ETTimer->start(1000);

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the code above not works of course, because "QTime::currentTime().toString("hh:mm:ss");" only returns the current time...

I wanna make a timer that starts from 00:00:00 and increase each second. But I dont know how to do it in QT. Please I really need your help!