title: Vb.Net RDLC sum field with same field's previous values
body: <p>To the point, I created a report using Report Wizard on Visual Studio 2010 Vb.Net.
  The layout is pretty much like this : </p>
  
  <pre><code>          DEBIT               CREDIT               BALANCE (FYI, this is an Expression)
        -----------------------------------------------------------------
           DValue1              CValue1           DValue1-CValue1 
           DValue2              CValue2           DValue2-CValue2+DValue1-CValue1
           etc...
        -----------------------------------------------------------------
  Total    DTotal               CTotal
  </code></pre>
  
  <p>I managed to create up to the DTotal and CTotal, what problematic is when I want to create the Balance with Expression.</p>
  
  <p>I tried this Expression, still no good.
      <code>=Sum(Fields!Debet.Value)-Sum(Fields!Credit.Value)+Previous(Fields!Debet)-Previous(Fields!Debet)</code>.
  This Expression returns an error that I should not use an aggregate within another aggregate.</p>
  
  <p>Please help me with this. There aren't many rdlc related tutorial even on google.</p>
  
  <p>Thank you so much.</p>