coordinal significant digits

[nitriles]

Hey,
using the moustracking:

#mouse coordinates
    picker = Qwt.QwtPlotPicker(Qwt.QwtPlot.xBottom,
                               Qwt.QwtPlot.yLeft,
                               Qwt.QwtPicker.NoSelection,
                               Qwt.QwtPlotPicker.CrossRubberBand,
                               Qwt.QwtPicker.AlwaysOn,
                               demo.canvas())
    picker.setTrackerPen(qt.QPen(qt.Qt.black))

#mouse coordinates
    picker = Qwt.QwtPlotPicker(Qwt.QwtPlot.xBottom,
                               Qwt.QwtPlot.yLeft,
                               Qwt.QwtPicker.NoSelection,
                               Qwt.QwtPlotPicker.CrossRubberBand,
                               Qwt.QwtPicker.AlwaysOn,
                               demo.canvas())
    picker.setTrackerPen(qt.QPen(qt.Qt.black))

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how can i change the number of significant digits? I only want 2 places behind the decimal, %.2f ???
Thanks