Question to Grid Chart

[#1]

Hi, today I have a quetsion for a grid chart.

My dimensions are Country & Balance date,

so I'll display in a Grid Chart each Country with a specific value per Balance Date. To this point it's no problem. but now I wan't to display the average value for all countries within the chart of each country. You know what I mean?

In each chart I'll insert a second line, showing the average value of all countries together.

within an ordinary chart it is no problem: sum({1}....) But this didn't work within a grid chart.

Is there any chance to do that?

Thanks & best regards

Stefan