I would like to create a xy-scatter chart for a dataset with two different
x-axis.

I have one set of data, but I need to plot it against two axis,
"concentration" and "dilution factor". The dilution (and therefore the
concentration) is not linear, so a line chart will display the data
"distorted" or "skewed".

I tried the tip from bj (9/9/2005 4:44 AM PST, to the question "Line chart
or scatter chart??")
there can be two x axis in a scatter chart.
first select one of the data series and <axis select secondary
next in <chart<chart options<axis select secondary x axis.
by duplicating the data. But I could not find any possibility to enable the
"second category (x) axis", it stays disabeld even with two data series.

(I'm using Excel 2003.)