Make your chart with at least one series on the secondary axis, as
you've done. Right click on the chart, choose Chart Options, click on
the Axes tab. Uncheck the secondary Y axis and check the secondary X axis.
Can't believe I hadn't seen that before for as long as
I've been frustrated about it. But then again, none of my
collegues have either.... BTW: great web site!
-OkieViking