How to add vertical line or point to a XY chart with 2 series?

[Andrés Monroy-Hernández <amonroy mit edu>]

Hello,

I would like to add a vertical line or at least a "Point" to this XY
chart in this spreadsheet:
http://dl.getdropbox.com/u/285483/tmp/pct_remix_per_day.gnumeric

The first column represents dates and the two other columns represent
values on each date.

As you can see from the properties of the chart, I added a "Point" to
one of the series but it does not show up.

Any ideas would be greatly appreciated.

Thanks.

-- 
Andrés