Line chart - overall line in addition to legend - possible?

[po]

Hi,

Have following scenario.

Line chart with legend of nation (scotland, wales, englen, n ieland)  showing sales over time.

i.e. 4 lines.

Is it posisble to add extra line to same chart which average over the 4 areas?

tried analysis/ avergae/media but just gives straight line.

Thanks

[amitchandak]

@po , You can get an Average in total

AveragX(values(Table[nations]),[sales]) 

where sales is measure sum of sales amount

[po]

Thanks for reply.  

When I try add in average, it just shows dropdown list with the one value (the measure in line chart) which woud have hoped would take average of the various countries but just has staight horizontal line (i.e. doesn't seem to allow you to point average to a user defined average formula.