Darin,

You can use parameters to drive a couple of calculated measures for the plot.  I've attached a workbook here to demonstrate.  The first tab is the simple setup, the second tab "synchronizes" the axes using hidden reference lines (see http://community.tableau.com/message/236674) so that you can make accurate comparisons.

Note that the parameters can be initialized with values from the country field, but are not dynamically updated with values from that field.

Regards,

Joshua

Also don't forget to add Month to detail or pages so you can see the Monthly Average Sales.

Good catch!

Actually, a very good catch as it made me realize I needed to adjust the country average calculations to return 0 instead of NULL.  Otherwise, marks were not showing up when one country didn't have sales in a given month.  Thanks!

I've updated the workbook and screenshot in the original reply.

Regards,

Joshua

No problem and well done.

You're welcome!