title: Count how many values have duplicates in a column
body: <p>I have values in a column like:</p>
  
  <pre><code>08FHI800
  08FHI800
  08FHI800
  07FJM933
  07FJM933
  89MNA900
  </code></pre>
  
  <p>I need a formula that tells me how many items in the column have corresponding duplicates.  In this case, it would be 2.  </p>