avoiding zoom out

[mastupristi]

I have a QwtPlot and QwtPlotMagnifier. I don't want to zoom out beyond curve limits. For example in my curve is in [-10.0, +10.0] I don't wanto to zoom out to show [-20, +20].
In the same way I don't want to zoom in beyond a certain scale of magnification.
How can I set magnification bounds?

thanks

[mastupristi]

I have defined derived class from QwtPlotMagnifier. I have reimplemented rescale() method to avoid zooming out

bye