How to implement one-dimensional zoom

I need a little help, and I can't find anything in the examples or by searching the forum.

I have a QwtPlot for which I want to implement zooming on the x-axis only; the y-axis will be automatically scaled to the minimum / maximum for the selected x range.

I can't figure out how to set the SelectionMode, SelectionType, RubberBand, etc. so I get a horizontal rubber band line that is constrained to move only in the x-direction. Everything I have tried generally gives me nothing on screen at all, and often no signals.

Is there a tutorial, FAQ, example, anything that shows how to do this?

Thanks,

David