I discovered that changing the type of x-axis under Chart Options to Category
instead of Time-Scale gets around the problem of inserting a vertical line on
a column chart with monthly time-series data. And instead of using dates for
the vertical line x-values, indicate the number of columns to the left of the
vertical line + 0.5.

For example, I have monthly data from Jan 2003 - Dec 2006 and I want to
insert a vertical line between the June 2006 and July 2006 columns. After
changing the type of x-axis to Category (and making any necessary format
changes), I paste the following series onto the chart:

Data
30.5 0
30.5 1

I then plot this series on the secondary y-axis with range 0-1 and change
the type of chart for the series to XY (Scatter) with data points connected
by lines. I use 30.5 for the x-value because I want the line to appear
between the 30th and 31st months/columns.

This procedure should work as long as you're using data with regular time
intervals and no missing data points have to be imputed.

"Tyler H" wrote:

I am attempting to add a vertical line to a dynamic column chart. I've
followed the steps described by Jon Peltier at
http://peltiertech.com/Excel/Charts/...ertSeries.html
This procedure works fine until I change the base unit on the x-axis to
"Days." This causes the columns to turn into vertical lines (since each
monthly observation is really for, e.g., 6/1/2007).

If I leave the x-axis as monthly and then add the secondary x-axis for the
vertical (xy scatter) line, the scale on the secondary x-axis goes from
1/1/1900 - 12/1/2036, which shoves my vertical line far to the right of where
I need it to appear on the primary x-axis.

I realize I can manually alter the min and max of the secondary x-axis to be
the (numerical) equivalents of my min and max for the primary x-axis. But
since this is a dynamic chart, I'd prefer to have the scaling set
automatically instead of manually adjusting it every few months.

Any suggestions will be greatly appreciated.