Usign ADO, this is how you'd do such a thing.  I've experienced a few very obscure problems using DAO (usually on multiuser/networked databases) which ADO doesn't seem to have a problem with.

Function UpdateTable()

   Dim rsWork As ADODB.Recordset
   Dim strSQL As String
   
   strSQL = "SELECT * FROM tMyTable;"
   Set rsWork = New ADODB.Recordset
   rsWork.Open strSQL, CurrentProject.Connection, adOpenDynamic, adLockOptimistic
   If rsWork.BOF = False Or rsWork.EOF = False Then
       rsWork.MoveFirst
       Do While rsWork.EOF = False
           If rsWork("ThisField") > rsWork("ThatField") Then
               rsWork("SomeOtherField") = "This record changed"
               rsWork.Update
           End If
           rsWork.MoveNext
       Loop
   Else
       MsgBox ("This recordset is empty")
   End If
   rsWork.Close
   Set rsWork = Nothing
   
End Function

This is nearly always a Bad Thing To Do -- if a value depends only on other
fields, then it should not be in the table at all, but in the query.

Try reading about Second Normal Form.

HTH

Tim F