Chart with percentage in Tablix

Hi there,

I am pretty new with SRRS and trying to make a chart in the tablix. I am able to make the chart to present the number of server region on the chart like something below:

But, rather than presenting number of instant, I would like the percentage of each server region over the country on each month. How could I do that. I am checking around but it will not work:

1. I tried to divide it over sum(Fields!server.value, "DataSet1") but this is returning data of whole database rather than for each specific month.

2. I tried to divide it over sum(Fields!server.value, "Chart2_CategoryGroup") but this will be returning back data for that specific server region and not whole country data.

Please help...