A problem about right click zooming

I have a issue with right click zoom out. I want to zoom out even after "zoomer->zoomRectIndex()" being 0. Before attaching a signal I used "setAxisAutoScale(QwtPlot::xBottom, true);" and "setAxisAutoScale(QwtPlot::yLeft, true);". I used "zoomer->setZoomBase(true);" after attaching my last signal. All thing is well till zoomer->zoomRectIndex()==0. But I need I can zoom out many time after this too. For Example after being zoomer->zoomRectIndex()==0, by right clicking again, xBottom and yLeft scales to be 2 times more than before zooming out scales.