title: Custom functions error: 'the expression cannot be used in a calculated column'
body: <p>In Access 2010 I am trying to use custom VBA functions in a calculated column. I get 'the expression cannot be used in a calculated column'. </p>
  
  <p>Here are my steps:</p>
  
  <ol>
  <li>Launch Access 2010.</li>
  <li>Create a new database "DB".</li>
  <li>Create a table "Table1" with a text column "Column1". Create a test row with "hello" in Column1.</li>
  <li>On "Create" ribbon, click "Module" at the upper-right corner, which launches VBA editor.</li>
  <li>In VBA editor "Project" window, there are two projects "ACWZTOOL" and "DB". Choose "DB" and select "Insert" -> "Module".</li>
  <li><p>Write the following code:</p>
  
  <pre><code>Public Function TestFunc() As String
      TestFunc = "test"
  End Function
  </code></pre></li>
  <li>"Debug" -> "Compile DB" passed, "Save" and closed VBA editor. Now "Module1" appears in "Modules" tab in the left pane.</li>
  <li>In Table1, create a calculated column "Column2", with expression "Len([Column1])", the column works properly with the value in test row being 5.</li>
  <li>Change the expression to "TestFunc()", the error pops up.</li>
  <li>I tried a few other built-in functions, it seems only the "basic" ones are supported in expression builder. E.g. "InStrRev()" is also not recognized.</li>
  </ol>