title: RDLC calculate running totals?
body: <p>I am struggling to get a running sum to work on a report. What I want is the following:</p>
  
  <pre><code>Product    Qty1   Qty2  Total  RunningTotal
  ABC123     100    200   300    300
  DEF321     50     100   150    450
  XYZ123     -100   -150  -250   200
  </code></pre>
  
  <p>The total column is an expression like</p>
  
  <p><code>=ReportItems!Qty1.value + ReportItems!Qty2.Value</code></p>
  
  <p>For running total I have tried many different things, most of which tell me that it has to be in a header or footer. The obvious expression which I thought would work is </p>
  
  <p><code>=ReportItems!Total.Value + previous(ReportItems!Total.Value)</code> </p>
  
  <p>but that doesnt work.</p>
  
  <p>Can anyone explain what I am doing wrong here?</p>
  
  <p>Cheers
  Dean</p>