title: Sql Server Reporting Services: how to calculate percentage difference?
body: <p>I have a report in SQL Server reporting services, grouped by a column "ProdType".
  Each row is a Year. How to calculate Subtotals but with the Difference of value instead the Sum ?</p>
  
  <p>At the moment the expression is : =Sum(Fields!Tot.Value).<br>
  Is there a Difference function ?</p>
  
  <p>Thank you</p>
  
  <p>EDIT: In particular, i've only 2 records per group: </p>
  
  <pre><code>Prodtype         Year         Value
  A                2000         10
  A                2001         12
    Diff.                       +20%
  
  B                2000         5
  B                2001         10
    Diff.                       +100%
  </code></pre>
  
  <p>My main problem is to create the "Diff." row with the percentage increment / decrement!</p>