Rownumber() function of RDLC report isn't correct

Question

Below figure is my report. This tablix has 10 row from dataset.

It's grouped by TOOL_CODE and TYPE for get count. At "Count" Column is use this expression ..

   = Count("Detials")  

"Detials" is a name of group(by TOOL and TYPE)

And No.Column I use expression by Rownumber() function like these

   = Rownumber(Nothing)

It's wrong because Rownumber() refer to items in dataset. It's not count from row which is display.

Answer 1

I solved this problem.

At "No." Column use this expression

  =RunningValue(CountDistinct("TableName"),Count,"TableName")