title: Multiple Lines in Excel, need a Formula to calculate diferences
body: <p>I have an inventory spread sheet.<br>
  There are 5700 rows all up to column "I".<br>
  These rows have part numbers in column "A".<br>
  Column "I" contains the cost of that part based on a quantity of parts listed elsewhere in the table.   </p>
  
  <p>With me so far?</p>
  
  <p>Lets say Row "1" contains a part number 9FH-01010 and column "I" gives a dollar value based on other criteria, (number of parts BEFORE Inventory).<br>
  Row "2" would be the same with the exception that row "2" is based on the dollar value AFTER inventory.</p>
  
  <p>Is there a formula that could identify like cells in column "A" and then calculate the difference in dollar value of "I" and then place that answer in column "J"?</p>
  
  <p>Here's the kicker, there are some part numbers that have only 1 entry. </p>
  
  <p>Example:</p>
  
  <pre><code>"A1" = 9FH01010     "I1" = 5000.00     "J1" = -2500.00     
  "A2" = 9FH01010     "I2" = 2500.00
  
  "A3" = 9FH20202     "I3" = 4300.00
  
  "A4" = 9FH30303     "I4" = 2000.00     
  "A5" = 9FH30303     "I5" = 4000.00     "J5" = 2000.00
  </code></pre>
  
  <p>Any help on this is appreciated.</p>