DataTable Expression Column

My DataGrid is bound to a DataSet, with following columns: Description, CashExp, CreditExp,Frequency On run time, I am adding two new DataColumn “AnnualCash” and “AnnualCredit” and defining Expression property to give product of two columns, as follows Dim dc As DataColumn dc = New DataColumn("AnnualCash", GetType(System.Single)) dc.Expression = " CashExp * Frequency" myDataSet.Tables("ClientExpenses").Columns.Add(dc) dc = New DataColumn("AnnualCredit", GetType(System.Single)) dc.Expression = " CreditExp * Frequency" myDataSet.Tables("ClientExpenses").Columns.Add(dc) The only problem I am getting is when CashExp or CreditExp or Frequency is changed the value of derived column is not changed (calculated) until user changes the row either by tab or arrow keys. How can I change this behaviour so that the derived columns gets calculated when user edit values in a cell.