jw wrote:
I have a series that I chart as a column, "Precipitation"
and three series that I chart as XY Scatter, "Plant Cover
1"...

I created the chart as a column chart and when I change
each of the "Plant Cover" series to an XY Scatter, Excel
chooses the "Precipitation" column to plot on the primary
axis. I would like "Precipitation" on the secondary axis
so the chart matches the format of my other charts.

I have tried to select the XY Scatter series and put them
on the primary axis, but the column just disappears.

I have tried starting with an XY Scatter chart first
also, and then changing the "Precipitation"

Sometimes I am able to get the graph I am looking for
with experimentation. But I never find a method I can
write down and use the next time. For example, when I
try to put "Precipitation" on the second axis and select
Secondary Y and Secondary x axes, sometimes the column
charts from the top of the chart down.

How can I find a consistent method?

This worked for me.

Create the chart with all series as XY scatter. Select the "Precipitation"
series, change it to the secondary axis. Right-click the chart and select
Chart Options | Data tab. Enable the secondary X axis. Now change the
Precipitation series to column.

The columns originate from the top, but I presume from your comments that
the matching charts are also like that.

Hope this helps.

Dave
dvt at psu dot edu